This paper was devoted to the study of the so-called nonlinear higher Lie n-derivation of triangular algebras T, where n is a nonnegative integer greater than two. Under some mild conditions, we proved that every nonlinear higher Lie n-derivation by local actions on the triangular algebras is of a standard form. As an application, we gave a characterization of higher Lie n-derivation by local actions on upper triangular matrix algebras, block upper triangular matrix algebras and nest algebras, respectively.
Citation: Xinfeng Liang, Mengya Zhang. Triangular algebras with nonlinear higher Lie n-derivation by local actions[J]. AIMS Mathematics, 2024, 9(2): 2549-2583. doi: 10.3934/math.2024126
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This paper was devoted to the study of the so-called nonlinear higher Lie n-derivation of triangular algebras T, where n is a nonnegative integer greater than two. Under some mild conditions, we proved that every nonlinear higher Lie n-derivation by local actions on the triangular algebras is of a standard form. As an application, we gave a characterization of higher Lie n-derivation by local actions on upper triangular matrix algebras, block upper triangular matrix algebras and nest algebras, respectively.
In this paper, we assume that A is an unital algebra over commutative ring R and Z(A) is the center of A. The main purpose of this paper is to study the structure of nonlinear higher Lie n-derivation by local actions on triangular algebras. To achieve this goal, we first introduce some definitions related to nonlinear higher Lie n-derivation by local actions.
Let N be the set of all nonnegative integers and Δ={δm}m∈N be a family of R-linear (resp. nonlinear) mapping δm:A→A on A such that δ0=idA. Δ is called:
a) a (resp. nonlinear) higher derivation if
δm(xy)=∑i+j=mδi(x)δj(y) | (1.1) |
for all x,y∈A and for each n∈N;
b) a (resp. nonlinear) higher Lie n-derivation if
δm(Pn(x1,⋯,xn))=∑i1+⋯+in=mPn(δi1(x1),δi2(x2),⋯,δin(xn)), | (1.2) |
where Pn(x1,⋯,xn)=[Pn−1(x1,⋯,xn−1),xn] is a polynomial defined by induction with variables x1,⋯,xn for all x1,⋯,xn∈A; the symbol [x1,x2]=x1x2−x2x1 is called the Lie product. If Eq (1.2) holds only under condition x1⋯xn=0 for all x1,⋯,xn∈A and for each m,n∈N, Δ={δm}m∈N is said to be higher Lie n-derivation by local actions. That is, Δ is said to be higher Lie n-derivation by local actions if every mapping δm satisfies the equation
δm(Pn(x1,⋯,xn))=∑i1+⋯+in=mPn(δi1(x1),δi2(x2),⋯,δin(xn)) | (1.3) |
for all x1,⋯,xn∈A with x1⋯xn=0 and m,n∈N. It should be noted that the study of derivatives satisfying local properties originated from papers[1,2]. For n=2,3 and any positive integer m in (1.2) (resp. (1.3)), Δ is referred to as Lie high derivation (resp. by local actions) and Lie triple high derivation (resp. by local actions), respectively. If m=1 and any positive integer n in Eq (1.2) (resp. (1.3)), then the mapping δ1 is called Lie n-derivation (resp. by local actions). Therefore, in the sense of Herstein Lie type mapping, higher Lie n-derivation is a natural extension of Herstein Lie type mappings. From the structure of maps (1.1)–(1.3), it can be seen that the sum of the higher derivations and the central map of annihilation Pn(x1,⋯,xn) is still higher Lie n-derivation (resp. by local actions), for all x1,⋯,xn∈A (resp. with x1⋯xn=0). If every higher Lie n-derivation has this decomposition form, it is said that higher Lie n-derivation has a standard form. Under this framework, some special situations of (nonlinear) higher Lie n-derivation have been studied by many scholars, (nonlinear) Lie triple derivation in paper [3,4], (nonlinear) Lie higher derivations in papers [5,6,7], Lie higher derivations studied in paper[8], higher derivations [9,10] etc.
In the author's knowledge system, the study of the structure of higher Lie n-derivation by local actions satisfying Eq (1.3) over rings or algebras has attracted many scholars to study among the many extensions of Lie-n derivation (see [11,12,13,14,15,16,17,18,19]. In 2011, Ji and Qi[11] studied the structural form of linear Lie derivation by local actions on triangular algebras (in (1.3), where (m,n)=(1,2)), and proved that each Lie derivation by local action has a standard form. Subsequently, Lin[12] extended this to three Lie higher derivation by local actions (in (1.3), m was an arbitrary positive integer and n = 2) and obtained that each Lie derivation by local action has a standard form. At the same time, in recent years, the authors and collaborators have found that many scholars have studied the structural problems of some special cases of nonlinear higher Lie n-derivation by local actions defined by equation (1.3) on rings or algebras. Liu in [15] worked the structure of Lie triple derivations by local actions satisfying the condition x1x2x3∈Ω={0,p} (in Relation (1.3) with n=3 and m=1), where p is a fixed nontrivial projection of factor von Neumann algebra M with dimension greater than one. He showed that every Lie triple derivations by local actions be of standard form, for von Neumann algebra with no central abelian projections M. In 2021, Zhao[16] considered the structure of nonlinear Lie triple derivations by local actions (in Relation (1.3) with n=3 and m=1) on triangular algebra. He confirmed that every nonlinear Lie triple derivations by local actions be of standard form. On the basis of his work[16], the first authors and collaborators extended the structure of nonlinear Lie triple derivations [16] to nonlinear Lie triple higher derivations by local actions[17] (condition: For arbitrary m∈N and n=3 in (1.3)), and proved that each nonlinear Lie triple higher derivation by local actions has a standard form (see Eq (1.4)) under the same conditions as Zhao[16]. Inspired by the above results[16,17], it is natural to consider the structure form of the higher Lie n-derivation by local actions (the case: m∈N and n>2 in Eq (1.3)) on triangular algebras. The results of this paper generalize Zhao[16] and Liang[17] to a more general form: For arbitrary m∈N and n≥3. It should be noted that we are temporarily unable to find a method to prove the structural form of nonlinear Lie higher derivations by local actions on triangular algebras. This is also an open problem left over in this article.
In this paper we established the higher Lie n-derivation by local actions (n>2) on triangular algebras. Let T be a triangular algebra over a commutative ring R. Under some mild conditions, we prove that if a family Δ={δm}m∈N of nonlinear mappings δm on T satisfies the condition (1.3), then there exists an additive higher derivation D={χm}m∈N and a nonlinear mapping hm:T→T on T vanishing all Pn(x1,⋯,xn) for all x1,⋯,xn∈T with x1⋯xn=0, such that
δm(x)=χm(x)+hm(x). |
Next, we immediately apply our results to typical examples of triangular algebra: Upper triangular matrix algebras, block upper triangular matrix algebras and nest algebras. At the same time, our conclusion generalizes the conclusions of papers [16,Theorems 2.1 and 2.2] and [17,Theorems 1 and 3].
In this part, we introduce some basic theories of triangular algebra. In 2001, triangular algebra was first introduced by Cheung[20].
Based on algebra A with identity 1A and algebra B with identity 1B, defined on ring R and faithful (A,B)-bimodule M, for a∈A, aM={0} implies a=0 and for b∈B, Mb={0} implies b=0. Cheung introduced a set
T=[AM0B]={[am0b]|∀ a∈A,m∈M,b∈B}. |
According to the addition and multiplication properties of matrices, set T is an associative and noncommutative R-algebra. This algebra is called triangular algebra. The most classical examples of triangular algebras are upper triangular matrix algebras, nest algebras and block upper triangular matrix algebras (see [7,20,21] for details). Furthermore, the center Z(T) of T is (see [20,22])
Z(T)={[a00b]|am=mb, ∀ m∈M}. | (♡) |
Let us define two natural R-linear projections πA:T→A and πB:T→B by
πA:[am0b]⟼aandπB:[am0b]⟼b. |
It follows from simple calculation that πA(Z(T)) is a subalgebra of Z(A) and that πB(Z(T)) is a subalgebra of Z(B). Additionally, there exists a unique algebraic isomorphism τ:πA(Z(T))⟶πB(Z(T)) such that am=mτ(a) for all a∈πA(Z(T)) and for all m∈M.
Regarding the center of algebra A, we need to make the following notes. In 2012, Benkovic and Eremita[23] introduced the following useful condition: For an arbitrary R-algebra A:
[x,A]∈Z(A)⟹x∈Z(A), ∀x∈A. | (♢) |
This amounts to saying that
[[x,A],A]=0⟹[x,A]=0∈Z(A), ∀x∈A. |
Note that (♢) is equivalent to the condition that there does not exist nonzero central inner derivations on A. The usual examples of algebras satisfying (♢) are upper triangular matrix algebras, block upper triangular matrix algebras and nest algebras (see [24]).
This section examines the structure of Lie n-derivations on triangular algebras by local operations at zero product. To put it more specifically, we demonstrate that any nonlinear Lie n-derivations by local actions at zero product have a standard form under mild conditions after first demonstrating that the nonlinear Lie n-derivations by local actions at zero product are an additive mapping of module Z(T). The information will provide the generalized version matching to [16,Theorems 2.1 and 2.2].
Theorem 3.1. Let T=[AMOB] be a triangular algebra satisfying πA(Z(T))=Z(A) and πB(Z(T))=Z(B)). Suppose that a mapping Ln:T→T (n≥3) is a nonlinear map satisfying
Ln(Pn(x1,x2,⋯,xn))=n∑i=1Pn(x1,x2,⋯,δ1(xi),⋯,xn) |
for all x1,x2,⋯,xn∈T with x1x2⋯xn=0, then for every n∈N,
Ln(x+y)−Ln(x)−Ln(y)∈Z(T) |
for all x,y∈T.
For convenience, let us write A11=A, A22=B and A12=M, then triangular algebra T=[AMOB] can be rewritten by T=[A11A12OA22].
In order to facilitate readers' understanding, we will divide the proof process into the following lemmas.
Lemma 3.1. [16,Claim 1] Let aii∈Aii,i∈{1,2}. If a11m12=m12a22 for all m12∈A12, then a11⊕a22∈Z(T).
Lemma 3.2. Ln(0)=0.
In particular, take xi=0 in formula (1.1) for i∈{1,2,⋯,n}.
Lemma 3.3. Let aij∈Aij, for 1≤i≤j≤2, then
1) Ln(a11+a12)−Ln(a11)−Ln(a12)∈Z(T);
2) Ln(a22+a12)−Ln(a22)−Ln(a12)∈Z(T).
Proof. 1) Let a11∈A11 and a12,c12∈A12. Denote T=Ln(a11+a12)−Ln(a11)−Ln(a12). It is clear that the elements a11,a12,c12 and idempotents p1,p2 satisfy the relations a12(a11+c12)p1p2 ⋯p2⏟n−3 copies=0=a12a11p1p2⋯p2⏟n−3 copies=0=a12c12p1p2⋯p2⏟n−3 copies, then we have
Ln(a11a12)=Ln(Pn(a12,a11+c12,p1,p2⋯p2⏟n−3 copies))=Pn(Ln(a12),a11+c12,p1,p2⋯p2⏟n−3 copies)+Pn(a12,Ln(a11+c12),p1,p2⋯p2⏟n−3 copies)+Pn(a12,a11+c12,Ln(p1),p2⋯p2⏟n−3 copies)+n∑i=4Pn(a12,a11+c12,p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2), |
and on the other hand, we obtain
Ln(a11a12)=Ln(Pn(a12,a11,p1,p2,⋯,p2⏟n−3 copies))+Ln(Pn(a12,c12,p1,p2,⋯,p2⏟n−3 copies))=Pn(Ln(a12),a11+c12,p1,p2⋯p2⏟n−3 copies)+Pn(a12,Ln(a11)+Ln(c12),p1,p2,⋯,p2⏟n−3 copies)+Pn(a12,a11+c12,Ln(p1),p2,⋯,p2⏟n−3 copies)+n∑i=4Pn(a12,a11+c12,p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2). |
The above two equations can be lead to Pn(a12,T,p1,p2⋯p2⏟n−3 copies)=0, which is p1Tp1a12=a12p2Tp2. It follows from Lemma 3.1 that
p1Tp1⊕p2Tp2∈Z(T). | (3.1) |
Let's prove that p1Tp2=0. Since the elements a11,a12 and idempotents p1,p2 satisfy the relation p2(a11+a12)p1p2 ⋯p2⏟n−3 copies=0=p2a11p1p2⋯p2⏟n−3 copies=0=p2a12p1p2⋯p2⏟n−3 copies, we study the form of elements Ln(a12) form two perspectives, namely,
Ln(a12)=Ln(Pn(p2,a11+a12,p1,p2⋯p2⏟n−3 copies))=Pn(Ln(p2),a11+a12,p1,p2⋯p2⏟n−3 copies)+Pn(p2,Ln(a11+a12),p1,p2⋯p2⏟n−3 copies)+Pn(p2,a11+a12,Ln(p1),p2⋯p2⏟n−3 copies)+n∑i=4Pn(p2,a11+a12,p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2) |
and
Ln(a12)=Ln(Pn(p2,a11,p1,p2⋯p2⏟n−3 copies))+Ln(Pn(p2,a12,p1,p2⋯p2⏟n−3 copies))=Pn(Ln(p2),a11+a12,p1,p2⋯p2⏟n−3 copies)+Pn(p2,Ln(a11)+Ln(a12),p1,p2⋯p2⏟n−3 copies)+Pn(p2,a11+a12,Ln(p1),p2⋯p2⏟n−3 copies)+n∑i=4Pn(p2,a11+a12,p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2) |
for all a11∈A11,a12∈A12. It follows from the above two equations that Pn(p2,T,p1,p2⋯p2⏟n−3 copies)=0, which is p1Tp2=0. Combining with relation (3.1), we have
Ln(a11+a12)−Ln(a11)−Ln(a12)∈Z(T) |
for all aij∈Aij,1≤i≠j≤2.
Through a similar calculation process, we can conclude that (2) holds.
Lemma 3.4. Let a12,c12∈A12, then Ln(a12+c12)=Ln(a12)+Ln(c12).
Proof. Combining (−a12−p1)(p2+c12)p1p2⋯p2⏟n−3 copies=0 with Lemmas 3.2 and 3.3, we have
Ln(a12+c12)=Ln(Pn(−a12−p1,p2+c12,p1,p2,⋯,p2))=Pn(Ln(−a12)+Ln(−p1),p2+c12,p1,p2,⋯,p2)+Pn(−a12−p1,Ln(p2)+Ln(c12),p1,p2,⋯,p2)+Pn(−a12−p1,p2+c12,Ln(p1),p2,⋯,p2)+n∑i=4Pn(−a12−p1,p2+c12,p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2)=Ln(Pn(−a12,p2,p1,p2,⋯,p2))+Ln(Pn(−a12,c12,p1,p2,⋯,p2))+Ln(Pn(−p1,p2,p1,p2,⋯,p2))+Ln(Pn(−p1,c12,p1,p2,p2,⋯,p2))=Ln(a12)+Ln(c12) |
for all a12,c12∈A12.
Lemma 3.5. Let aii∈Aii,i∈{1,2}, then δ1(aii+bii)=δ1(aii)+δ1(bii)+Zaii,bii for some central element Zaii,bii∈Z(T).
Proof. We will only prove the case with i=1. The proof of the case i=2 can be proved through a similar process.
Let a11,b11∈A11,w12∈A12. Denote U=δ1(a11+b11)−δ1(a11)−δ1(b11). It follows from w12p1(a11+b11)p2⋯p2⏟n−3 copies=w12p1a11p2⋯p2⏟n−3 copies=w12p1b11p2⋯p2⏟n−3 copies=0 that
Ln((a11+b11)w12)=Ln(Pn(w12,p1,(a11+b11),p2,⋯,p2))=Pn(Ln(w12),p1,(a11+b11),p2,⋯,p2)+Pn(w12,Ln(p1),(a11+b11),p2,⋯,p2)+Pn(w12,p1,Ln(a11+b11),p2,⋯,p2)+n∑i=4Pn(w12,p1,(a11+b11),p2,⋯,Ln(p2)⏟i−th component,⋯,p2) |
and
Ln((a11+b11)w12)=Ln(a11w12)+Ln(b11w12)=Ln(Pn(w12,p1,a11,p2,⋯,p2))+Ln(Pn(w12,p1,b11),p2,⋯,p2))=Pn(Ln(w12),p1,(a11+b11),p2,⋯,p2)+Pn(w12,Ln(p1),(a11+b11),p2,⋯,p2)+Pn(w12,p1,Ln(a11)+Ln(b11),p2,⋯,p2)+n∑i=4Pn(w12,p1,(a11+b11),p2,⋯,Ln(p2)⏟i−th component,⋯,p2). |
By observing the two equations above, we have Pn(w12,p1,U,p2,⋯,p2)=0, which is w12U=Uw12. It follows from Lemma 3.1 that
p1Up1⊕p2Up2∈Z(T). | (3.2) |
In the rest of the lemma, we prove that the equation p1Up2=0 holds.
Since the equations (a11+b11)p2⋯p2⏟n−1 copies=a11p2⋯p2⏟n−1 copies=b11p2⋯p2⏟n−1 copies=0 hold, then we have
0=Ln(Pn(a11+b11,p2,⋯,p2⏟n−1 copies))=Pn(Ln(a11+b11),p2,⋯,p2⏟n−1 copies)+n∑i=2Pn(a11+b11,p2,⋯,Ln(p2)⏟i−th component,⋯,p2⏟n−1 copies) |
and
0=Ln(Pn(a11,p2,⋯,p2⏟n−1 copies))+Ln(Pn(b11,p2,⋯,p2⏟n−1 copies))=Pn(Ln(a11)+Ln(b11),p2,⋯,p2⏟n−1 copies)+n∑i=2Pn(a11+b11,p2,⋯,Ln(p2)⏟i−th component,⋯,p2⏟n−1 copies). |
By observing the two equations above, we have Pn(U,p2,⋯,p2⏟n−1 copies)=0, which is p1Up2=0. Combining with Eq (3.2), we have
Ln(a11+b11)−Ln(a11)−Ln(b11)∈Z(T) |
for all a11,b11∈A11.
Lemma 3.6. Let aij∈Aij,1≤i≤j≤2, then Ln(a11+a12+a22)=Ln(a11)+Ln(a12)+Ln(a22)+Za11,a12,a22.
Proof. Let aij∈Aij,1≤i≤j≤2. Denote U=Ln(a11+a12+a22)−Ln(a11)−Ln(a12)−Ln(a22). With the help of the fact that equation (a11+a12+a22)c12p1p2⋯p2⏟n−3 copies=0 holds, we have
Ln(c12a22−a11c12)=Ln(Pn(a11+a12+a22,c12,p1,p2,⋯p2⏟n−3 copies))=Pn(Ln(a11+a12+a22),c12,p1,p2,⋯,p2⏟n−3 copies)+Pn(a11+a12+a22,Ln(c12),p1,p2,⋯,p2⏟n−3 copies)+Pn(a11+a12+a22,c12,Ln(p1),p2,⋯,p2⏟n−3 copies)+n∑i=4Pn(a11+a12+a22,c12,p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2⏟n−3 copies) |
and
Ln(c12a22−a11c12)=Ln(c12a22)+Ln(−a11c12)=Ln(Pn(a11,c12,p1,p2,⋯p2⏟n−3 copies))+Ln(Pn(a12,c12,p1,p2,⋯p2⏟n−3 copies))+Ln(Pn(a22,c12,p1,p2,⋯p2⏟n−3 copies))=Pn(Ln(a11)+Ln(a12)+Ln(a22),c12,p1,p2,⋯,p2⏟n−3 copies)+Pn(a11+a12+a22,Ln(c12),p1,p2,⋯,p2⏟n−3 copies)+Pn(a11+a12+a22,c12,Ln(p1),p2,⋯,p2⏟n−3 copies)+n∑i=4Pn(a11+a12+a22,c12,p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2⏟n−3 copies). |
By observing the two equations above, we have Pn(U,c12,p1,p2,⋯,p2⏟n−3 copies)=0, which is c12p2Up2=p1Up1c12. We have
p1Up1⊕p2Up2∈Z(T). | (3.3) |
For the rest, we prove the conclusion: p1Up2=0. It is clear that (a11+a12+a22)(−p1)p2⋯p2⏟n−2 copies=0. We then obtain
Ln(a12)=Ln(Pn(a11+a12+a22,−p1,p2,⋯,p2))=Pn(Ln(a11+a12+a22),−p1,p2,⋯,p2)+Pn(a11+a12+a22,Ln(−p1),p2,⋯,p2)+n∑i=3Pn(a11+a12+a22,−p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2) |
and
Ln(a12)=Ln(Pn(a11,−p1,p2,⋯,p2))+Ln(Pn(a12,−p1,p2,⋯,p2))+Ln(Pn(a22,−p1,p2,⋯,p2))=Pn(Ln(a11)+Ln(a12)+Ln(a22)),−p1,p2,⋯,p2)+Pn(a11+a12+a22,Ln(−p1),p2,⋯,p2)+n∑i=3Pn(a11+a12+a22,−p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2). |
By observing the two equations above, we have Pn(U,−p1,p2,⋯,p2⏟n−2 copies)=0, which is p1Up2=0. Combining with Eq (3.3), we have
Ln(a11+a12+a22)=Ln(a11)+Ln(a12)+Ln(a22)+Za11,a12,a22 |
for all aij∈Aij,1≤i≤j≤2.
Proof of Theorem 3.1: For arbitrary x,y∈T, elements x and y have decomposition form x=a11+a12+a22 and y=b11+b12+b22, where aij,bij∈Aij,1≤i≤j≤2. It follows from Lemmas 3.2–3.6 that there exists Cl∈Z(T), l∈{1,2,3,4,5}.
Ln(x+y)=Ln(a11+a12+a22+b11+b12+b22)=Ln(a11+b11)+Ln(a12+b12)+Ln(a22+b22)+C1=Ln(a11)+Ln(b11)+Ln(a12)+Ln(b12)+Ln(a22)+Ln(b22)+C1+C2+C3=Ln(a11+a12+a22)+Ln(b11+b12+b22)+C1+C2+C3+C4+C5. |
Therefore, we have
Ln(x+y)=Ln(x)+Ln(y)+C0 |
for some C0=C1+C2+C3+C4+C5∈Z(T).
Based on the almost additivity of Ln, we present the main theorem of this part to the readers as follows.
Theorem 3.2. Let T=[A11A12OA22] be a triangular algebra satisfying
i) πA11(Z(T))=Z(A11) and πA22(Z(T))=Z(A22);
ii) For any a11∈A11, if [a11,A11]∈Z(A11), then a11∈Z(A11) or for any a22∈A22, if [a22,A22]∈Z(A22), then a22∈Z(A22).
Suppose that a mapping Ln:T→T(n≥3) is a nonlinear mapping satisfying
Ln(Pn(x1,x2,⋯,xn))=n∑i=1Pn(x1,x2,⋯,Ln(xi)⏟i−th component,⋯,xn) |
for all x1,x2,⋯,xn∈T with ∏ni=1xi=0, then for every n∈N,
Ln(x)=dn(x)+fn(x) |
for all x∈T, where dn:T→T is an additive derivation, and fn:T→Z(T) is a nonlinear mapping such that fn(Pn(x1,x2,⋯,xn))=0 for any x1,x2,⋯,xn∈T with x1x2⋯xn=0.
In order to facilitate readers' understanding, we will divide the proof process into the following lemmas for explanation.
Lemma 3.7. With notations as above, we have
1) Ln(a12)∈A12;
2) p1Ln(p1)p1⊕p2Ln(p1)p2∈Z(T) and p1Ln(p2)p1⊕p2Ln(p2)p2∈Z(T);
3) Ln(p1)∈A12+Z(T) and Ln(p2)∈A12+Z(T).
Proof. Since the equation a12p1p1p2⋯p2=0 holds, we have
Ln(a12)=Ln(Pn(a12,p1,p1,p2,⋯,p2))=Pn(Ln(a12),p1,p1,p2,⋯,p2)+Pn(a12,Ln(p1),p1,p2,⋯,p2)+Pn(a12,p1,Ln(p1),p2,⋯,p2)+n∑i=4Pn(a12,p1,p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2)=p1Ln(a12)p2+2p1Ln(p1)a12−2a12Ln(p1)p2+(n−3)p1[a12,Ln(p2)]p2. | (3.4) |
According to above relation (3.4), we have Ln(a12)∈A12. Multiplying by p1 on the left side and p2 on the right side of the above Eq (3.4), we can obtain
−2p1[a12,Ln(p1)]+(n−3)p1[a12,Ln(p2)]p2=0 | (3.5) |
for all a12∈A12.
On the other hand, with the help of p2a12p1p2⋯p2⏟n−3 copies=0, we have
Ln(a12)=Ln(Pn(p2,a12,p1,p2,⋯,p2))=Pn(Ln(p2),a12,p1,p2,⋯,p2)+Pn(p2,Ln(a12),p1,p2,⋯,p2)+Pn(p2,a12,Ln(p1),p2,⋯,p2)+n∑i=4Pn(p2,a12,p1,p2,⋯,Ln(p2)⏟i−th component,⋯,p2)=−p1[Ln(p2),a12]p2+p1Ln(a12)p2−p1[a12,Ln(p1)]p2+(n−3)p1[a12,Ln(p2)]p2. | (3.6) |
According to (3.6), we have
(n−4)p1[a12,Ln(p2)]p2−p1[a12,Ln(p1)]p2=0. | (3.7) |
Combining (3.5) with (3.6), we have
p1[a12,Ln(p2)]p2=−p1[a12,Ln(p1)]p2. | (3.8) |
Using equalities (3.7) with (3.8) and considering the (n−1)-torsion-free properties of rings R, we conclude that
p1[a12,Ln(p2)]p2=p1[a12,Ln(p1)]p2=0 |
for all a12∈A12.
With the help of Lemma 3.1 that
p1Ln(p1)p1⊕p2Ln(p1)p2∈Z(T) and p1Ln(p2)p1⊕p2Ln(p2)p2∈Z(T), |
the structural characteristics of triangular algebra lead to conclusions
Ln(p1)=p1Ln(p1)p1+p1Ln(p1)p2+p2Ln(p1)p2∈A12+Z(T). |
Furthermore, we claim that this lemma holds.
Lemma 3.8. With notations as above, for all aii∈Aii,i∈{1,2}, we have
i) Ln(a11)∈A11+A12+Z(T), where p2Ln(a11)p2∈Z(A22);
ii) Ln(a22)∈A22+A12+Z(T), where p1Ln(a22)p1∈Z(A11);
iii) p1Ln(p1)p2+p1Ln(p2)p2=0.
Proof. In fact, it is clear that if a11p2⋯p2=0, we have
0=Ln(Pn(a11,p2,⋯,p2))=Pn(Ln(a11),p2,⋯,p2)+Pn(a11,Ln(p2),p2,⋯,p2)=p1Ln(a11)p2+a11Ln(p2)p2, |
which implies that
p1Ln(a11)p2+a11Ln(p2)p2=0 | (3.9) |
for all a11∈A11. Through similar calculations, combining with relation that if a22p1p1p2,⋯p2=0, we can show that
0=Ln(Pn(a22,p1,p1,p2,⋯,p2))=Pn(Ln(a22),p1,p1,p2,⋯,p2)+Pn(a22,Ln(p1),p1,p2,⋯,p2)=p1Ln(a22)p2+p1Ln(p2)a22, |
which implies
p1Ln(a22)p2+p1Ln(p2)a22=0 | (3.10) |
for all a22∈A22.
Now, we consider the following equation
0=Ln(Pn(p1,p2,⋯,p2))=Pn(Ln(p1),p2,⋯,p2)+Pn(p1,Ln(p2),⋯,p2)=p1Ln(p1)p2+p1Ln(p2)p2. |
That is,
p1Ln(p1)p2+p1Ln(p2)p2=0. | (3.11) |
In the light of equations a22a11a12p2⋯p2=0, we have
0=Ln(Pn(a22,a11,a12,p2,⋯,p2))=Pn(Ln(a22),a11,a12,p2,⋯,p2)+Pn(a22,Ln(a11),a12,p2,⋯,p2)=p1[[Ln(a22),a11],a12]p2+p1[[a22,Ln(a11)],a12]p2=p1[[Ln(a22),a11]p2+p1[a22,Ln(a11)],a12]p2. |
According to Lemma 3.1, we have
[Ln(a22),a11]+[a22,Ln(a11)]∈Z(T). |
Furthermore, we have
[p1Ln(a22)p1,a11]∈Z(A11) and [a22,p2Ln(a11)p2]∈Z(A22) |
for all a11∈A11,a22∈A22. Thanks to the assumption (ii), we have
p1Ln(a22)p1∈Z(A11) and p2Ln(a11)p2∈Z(A22) |
for all a11∈A11,a22∈A22. Therefore, this lemma holds.
Now, we define two mappings rn1:A11→Z(A11) and rn2:A22→Z(A22), as following
rn1(a11)=τ−1(p2Ln(a11)p2)+p2Ln(a11)p2 |
and
rn2(a22)=τ(p1Ln(a22)p1)+p1Ln(a22)p1 |
for all a11∈A11,a22∈A22, respectively. It follows from Lemma 3.11 that rn1:A11→Z(A11) satisfies the relation rn1(Pn(a111,a211,⋯,an11))=0 for all a111,a211,⋯,an11∈A11, with a111a211⋯an11=0 and rn2:A22→Z(A22) satisfying the relation rn2(Pn(a122,a222,⋯,an22))=0 for all a122,a222,⋯,an22∈A22 with a122a222⋯an22=0. Now, setting
hn(x)=rn1+rn2=τ−1(p2Ln(a11)p2)+p2Ln(a11)p2+τ(p1Ln(a22)p1)+p1Ln(a22)p1 |
for all x∈T, which satisfies the form x=a11+a12+a22, it is clear that hn(x)∈Z(T) and hn(Pn(x1,x2,⋯,xn))=0 for all x1,x2,⋯,xn∈T with x1x2⋯xn=0.
Let's define an important mapping:
Ψn(x)=Ln(x)−hn(x) |
for all x∈T.
Now, we can easily obtain the following lemmas.
Lemma 3.9. With notations as above, for all aij∈Aij,1≤i≤j≤2, we have
i) Ψn(0)=0;
ii) Ψn(A11)⊆A11+A12, Ψn(A22)⊆A22+A12;
iii) Ψn(A12)=Ln(A12); Ψn(pi)∈A12.
Lemma 3.10. With notations as above, for all aij∈Aij,1≤i≤j≤2, we have
i) Ψn(a11a12)=Ψn(a11)a12+a11Ψn(b12);
ii) Ψn(a12a22)=Ψn(a12)a22+a12Ψn(a22).
Proof. We now only prove the conclusion (i) and the proof of conclusion (ii) can be obtained by similar methods.
(i) It follows from a12a11p1p2⋯p2=0 that
Ψn(a11a12)=Φn(Pn(a12,a11,p1,p2,⋯,p2))=Pn(Φn(a12),a11,p1,p2,⋯,p2)+Pn(a12,Φn(a11),p1,p2,⋯,p2)=Pn(Ψn(a12),a11,p1,p2,⋯,p2)+Pn(a12,Ψn(a11),p1,p2,⋯,p2)=a11Ψn(a12)+a11Ψn(a12). |
By a similar method, the conclusion (ii) holds.
Lemma 3.11. With notations as above, for all aii,bii∈Aii,i∈{1,2}, we have Ψn(aiibii)=Ψn(aii)bii+aiiΨn(bii).
Proof. By Lemma 3.9, for all c12∈A12, we have
Ψn(a11b11c12)=Ψn(a11)b11c12+a11Ψn(b11c12)=Ψn(a11)b11c12+a11Ψn(b11)c12+a11b11Ψn(c12) |
and
Ψn(a11b11c12)=Ψn(a11b11)c12+a11b11Ψn(c12). |
Combining the two equations above, we have
(Ψn(a11b11)−Ψn(a11)b11−a11Ψn(b11))c12=0 |
for all a11,b11∈A11,c12∈A12. Since A12 is a faithful (A11,A22)-bimodule, we have
Ψn(a11b11)=Ψn(a11)b11+a11Ψn(b11) |
for all a11,b11∈A11.
After a similar calculation process, we can get
Ψn(a22b22)=Ψn(a22)b22+a22Ψn(b22) |
for all a22,b22∈A22.
Lemma 3.12. With notations as above, for all aii,bii∈Aii, we have
i) Ψn(a12+b12)=Ψn(a12)+Ψn(a12);
ii) Ψn(a11+a12)−Ψn(a11)−Ψn(a12)∈Z(T) and Ψn(a22+a12)−Ψn(a22)−Ψn(a12)∈Z(T);
iii) Ψn(aii+bii)=Ψn(aii)+Ψn(bii).
Proof. According to the above symbols, we can prove the lemma by using the relationship between mapping Ψn and mapping Ln. The details are as follows:
i). It is the direct result of Lemmas 3.4 and 3.9;
ii). It is the direct result of Lemma 3.3;
iii). According to the above Lemma 3.5, we have
Ψn(aii+bii)=Ψn(aii)+Ψn(bii)+Z(aii,bii) |
for some Z(aii,bii)∈Z(T). Let us consider the center element Z(aii,bii).
On the one hand,
Ψn((a11+b11)c12)=Ψn(a11c12)+Ψn(b11c12)=Ψn(a11)c12+a11Ψn(c12)+Ψn(b11)c12+b11Ψn(c12)=(Ψn(a11)+Ψn(b11))c12+(a11+b11)Ψn(c12), |
and on the other hand, we have
Ψn((a11+b11)c12)=Ψn(a11+b11)c12+(a11+b11)Ψn(c12) |
for all a11,b11∈A11,c12∈A12.
By observing the two equations above, we can obtain Z(a11,b11)c12=p1Z(a11,b11)p1c12=0 for all c12∈A12. Since A12 is a faithful (A11,A22)-bimodule, then p1Z(a11,b11)p1=0. Note that there is an algebra isomorphism τ:Z(A11)→Z(A22), and we can obtain p2Z(a11,b11)p2=τ(p1Z(a11,b11)p1)=0 and Z(a11,b11)c12=p1Z(a11,b11)p1+p2Z(a11,b11)p2=0. Therefore,
Ψn(a11+b11)=Ψn(a11)+Ψn(b11) |
for all a11,b11∈A11.
After a similar calculation process, we can get
Ψn(a22+b22)=Ψn(a22)+Ψn(b22) |
for all a22,b22∈A22.
According to the definition of Ψn and Theorem 3.1, we can get the following lemma immediately.
Lemma 3.13. Let aij∈Aij,1≤i≤j≤2, then Ψn(a11+a12+a22)=Ψn(a11)+Ψn(a12)+Ψn(a22)+Ca11,a12,a22.
Remark 3.1. Lemma 3.13 enables us to establish a mapping gn:T→T
gn(x)=Ψn(x)−Ψn(p1xp1)−Ψn(p1xp2)−Ψn(p2xp2) |
for all x∈T, then define a mapping dn:T→T by
dn(x)=Ψn(x)−gn(x) |
for all x∈T. It is easy to verify that each dn satisfies the following property:
1) dn(aij)=Ψn(aij);
2) dn(a11+a12+a22)=dn(a11)+dn(a12)+dn(a22)
for all aij∈Aij,i≤j∈{1,2}.
Now, we are in a position to prove our main theorem.
Proof of Theorem 3.1: It follows from the definitions of dn and gn that
Ln(x)=Φn(x)+hn(x)=dn(x)+gn(x)+hn(x)=dn(x)+fn(x), |
where fn(x)=gn(x)+hn(x) is a mapping from T into its center Z(T) for all x∈T.
For arbitrary x,y∈T, elements x and y have decomposition form x=a11+a12+a22 and y=b11+b12+b22, where aij,bij∈Aij,1≤i≤j≤2. It follows from Remark 3.1 that
dn(x+y)=dn(a11+a12+a22+b11+b12+b22)=dn(a11+b11)+dn(a12+b12)+dn(a22+b22)=dn(a11)+dn(b11)+dn(a12)+dn(b12)+dn(a22)+dn(b22)=dn(a11+a12+a22)+dn(b11+b12+b22). |
Therefore, we have
dn(x+y)=dn(x)+dn(y). |
Next, we prove that dn satisfies the Leibniz formula.
First, we should prove that
p1dn(a11)a22+a11dn(a22)p2=0 |
for all a11∈A11,a22∈A22.
In fact, because of a11a22p2⋯p2=0 and Eqs (3.9)–(3.10), we have
p1dn(a11)a22+a11dn(a22)p2=p1(Ψn(a11)+gn(a11))a22+a11(Ψn(a22)+gn(a22))p2=p1Ψn(a11)a22+a11Ψn(a22)p2=p1Ln(a11)a22+a11Ln(a22)p2=p1a11Ln(p2)a22+a11Ln(p1)a22=p1a11(p1Ln(p2)p2+p1Ln(p1)p2)a22=0 |
for all a11∈A11,a22∈A22.
In view of Lemmas 3.8–3.11, we have
dn(xy)=dn(a11b11+a11b12+a12b22+a22b22)=Ψn(a11b11)+Ψn(a11b12)+Ψn(a12b22)+Ψn(a22b22)=Ψn(a11)b11+a11Ψn(b11)+Ψn(a11)b12+a11Ψn(b12)+Ψn(a12)b22+a12Ψn(b22)+Ψn(a22)b22+a22Ψn(b22)+Ψn(a11b22)+a11Ψn(b22)=dn(a11)b11+a11dn(b11)+dn(a11)b12+a11dn(b12)+dn(a12)b22+a12dn(b22)+dn(a22)b22+a22dn(b22)+dn(a11)b22+a11dn(b22)=(dn(a11)+dn(a12)+dn(a22))(b11+b12+b22)+(a11+a12+a22)(dn(b11)+dn(b12)+dn(b22))=dn(a11+a12+a22)(b11+b12+b22)+(a11+a12+a22)dn(b11+b12+b22)=dn(x)y+xdn(y) |
for all x,y∈T.
Now, we consider the properties of the mapping fn:T→Z(T). For arbitrary x1,⋯,xn∈T with x1⋯xn=0, note that dn is an additive derivation of T, and we have
fn(Pn(x1,⋯,xn))=(Ln−dn)(Pn(x1,⋯,xn))=Ln(Pn(x1,⋯,xn))−dn(Pn(x1,⋯,xn))=n∑k=1Pn(x1,⋯,(Ln−dn)(xk),⋯,xn)=n∑k=1Pn(x1,⋯,fn(xk),⋯,xn)=0. |
Therefore, Theorem 3.1 holds.
This section focuses on researching higher Lie n-derivation at zero product on triangular algebras. We will provide the more advanced version (Theorems 4.1 and 4.2) that corresponds to Theorems 3.1 and 3.2. These conclusions generalize a few previous conclusions under the same presumptions, such as [16,Theorems 2.1 and 2.2] and [17,Theorem 1 and 3].
Theorem 4.1. Let T=[A11A12OA22] be a triangular algebra over (n−1)-torsion-free commutative ring R. Suppose that a sequence Δ={δm}m∈N of mappings δm:T→T is a nonlinear mapping
δm(Pn(x1,x2,⋯,xn))=∑i1+⋯+in=mPn(δi1(x1),δi2(x2),⋯,δin(xn)) | (4.1) |
for all x1,x2,⋯,xn∈T with x1x2⋯xn=0 and n≥3. If πA11(Z(T))=Z(A11) and πA22(Z(T))=Z(A22), then every nonlinear mapping δm is almost additive on T, which is
δm(x+y)−δm(x)−δm(y)∈Z(T) |
for all x,y∈T.
It is worth noting that the mapping δ1 in Theorem 4.1 is equal to the mapping Ln in Theorem 3.1. Based on this, we begin to prove theorem 4.1.
Assume that a sequence Δ={δm}m∈N of nonlinear mappings δm:T→T is a Lie-n higher derivation by local actions on triangular algebras T=[A11A12OA22]. We will use an induction method for the component index m. For m=1, δ1=Ln:T→T is a Lie n-derivation by local actions. According to Theorems 3.2 and 3.1, we obtain that a nonlinear Lie n-derivation δ1 by local actions meet the following attributes:
C1={δ1(0)=0,δ1(a11+a12)−δ1(a11)−δ1(a12)∈Z(T),δ1(a22+a12)−δ1(a22)−δ1(a12)∈Z(T);δ1(a12+a′12)=δ1(a12)+δ1(a′12);δ1(aii+aii)−δ1(aii)−δ1(aii)∈Z(T);δ1(a11+a12+a22)−δ1(a11)−δ1(a12)−δ1(a22)∈Z(T) |
for all aij∈A with i≤j∈{1,2}.
We assume that the result holds for all 1<s<m, m∈N, then nonlinear Lie n-derivation {δl}l=sl=0 satisfies the following
Cs={δs(0)=0,δs(a11+a12)−δs(a11)−δs(a12)∈Z(T),δs(a22+a12)−δs(a22)−δs(a12)∈Z(T);δs(a12+a′12)=δs(a12)+δs(a′12);δs(aii+aii)−δs(aii)−δs(aii)∈Z(T);δs(a11+a12+a22)−δs(a11)−δs(a12)−δs(a22)∈Z(T) |
for all aij∈A with i≤j∈{1,2}.
Our goal is to prove that the above conditions Cs also hold for m. The process of induction can be achieved through a series of lemmas.
Lemma 4.1. With notations as above, we have δm(0)=0.
Proof. With the help of condition Cs, we find that
δm(0)=δm(Pn(0,0,⋯,0))=∑i1+⋯+in=mPn(δi1(0),δi2(0),⋯,δin(0))=0. |
Lemma 4.2. With notations as above, we have
i) δm(a11+a12)−δm(a11)−δm(a12)∈Z(T);
ii) δm(a22+a12)−δm(a22)−δm(a12)∈Z(T)
for all aij∈A with i≤j∈{1,2}.
Proof. Here, we only prove that the conclusion i) holds and that the proof of conclusion ii) can be similarly obtained.
It is clear that x12(a11+x′12)p1p2⋯p2=x12a11p1p2⋯p2=0=x12x′12p1p2⋯p2 for all a11∈A11 and x12,x′12∈A12. On the one hand, we have
δm(a11x12)=δm(Pn(x12,(a11+x′12),p1,p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(x12),δi2(a11+x′12),δi3(p1),δi4(p2)⋯,δin(p2)), |
and on the other hand, we have
δn(a11x12)=δm(Pn(x12,a11,p1,p2,⋯,p2))+δm(Pn(x12,x′12,p1,p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(x12),δi2(a11),δi3(p1),δi4(p2)⋯,δin(p2))+∑i1+⋯+in=mPn(δi1(x12),δi2(x′12),δi3(p1),δi4(p2)⋯,δin(p2))=∑i1+⋯+in=mPn(δi1(x12),δi2(a11)+δi2(x′12),δi3(p1),δi4(p2)⋯,δin(p2)). |
By observing the two equations above and inductive hypothesis Cs for all 0≤s≤m−1, we arrive at
0=∑i1+⋯+in=mPn(δi1(x12),δi2(a11+x′12)−(δi2(a11)+δi2(x′12)),δi3(p1),δi4(p2)⋯,δin(p2))=∑i1+⋯+in=m,i2≠mPn(δi1(x12),δi2(a11+x′12)−(δi2(a11)+δi2(x′12)),δi3(p1),δi4(p2)⋯,δin(p2))+Pn(x12,δm(a11+x′12)−(δm(a11)+δm(x′12)),p1,p2,⋯,p2)=Pn(x12,δm(a11+x′12)−(δm(a11)+δm(x′12)),p1,p2,⋯,p2)=p1(δm(a11+x′12)−(δm(a11)+δm(x′12)))x12−x12(δm(a11+x′12)−(δm(a11)+δm(x′12)))p2 |
for all a11∈A11 and x12,x′12∈A12. It then follows from the center of algebra T that
p1(δm(a11+x′12)−(δm(a11)+δm(x′12)))p1+p2(δm(a11+x′12)−(δm(a11)+δm(x′12)))p2∈Z(T) |
for all a11∈A11 and x12∈A12.
In the following, we prove p1(δm(a11+x′12)−(δm(a11)+δm(x′12)))p2=0 for all a11∈A11 and x12∈A12.
With the help of p2(a11+x12)p1p2⋯p2⏟n−3 copies=0=p2a11p1p2⋯p2⏟n−3 copies, we have
δm(x12)=δm(Pn(p2,x12+a11,p1,p2,⋯,p2⏟n−3 copies))=∑i1+⋯+in=mPn(δi1(p2),δi2(x12+a11),δi3(p1),δi4(p2)⋯,δin(p2)) |
for all a11∈A11 and m12∈A12. On the other hand, we have
δm(x12)=δm(Pn(p2,x12,p1,p2,⋯,p2⏟n−3 copies))+δm(Pn(p2,a11,p1,p2,⋯,p2⏟n−3 copies))=∑i1+⋯+in=mPn(δi1(p2),δi2(x12)+δi2(a11),δi3(p1),δi4(p2)⋯,δin(p2)) |
for all a11∈A11 and x12∈A12. With the help of the above two equations and inductive hypothesis Cs, we have
0=∑i1+⋯+in=mPn(δi1(p2),δi2(x12+a11)−(δi2(x12)+δi2(a11)),δi3(p1),δi4(p2)⋯,δin(p2))=∑i1+⋯+in=m,i2≠mPn(δi1(p2),δi2(x12+a11)−(δi2(x12)+δi2(a11)),δi3(p1),δi4(p2)⋯,δin(p2))+Pn(p2,δm(x12+a11)−(δm(x12)+δm(a11)),p1,p2,⋯,p2)=Pn(p2,δm(x12+a11)−(δm(x12)+δm(a11)),p1,p2,⋯,p2)=p1(δm(a11+x12)−(δm(a11)+δm(x12)))p2 |
for all a11∈A11 and x12∈A12. Therefore, we obtain that the conclusion (i) holds.
For conclusion (ii), taking into accounts the relations x12(b22+x′12)p1p2⋯p2⏟n−3 copies=x12x′12p1p2⋯p2⏟n−3 copies=x12b22p1p2⋯p2⏟n−3 copies=0, by an analogous manner one can show that the conclusion
δm(b22+x′12)−(δm(b22)+δm(x′12))∈Z(T) |
holds for all b22∈A22 and x12,x′12∈A12.
Lemma 4.3. With notations as above, we have δn(x12+x′12)=δn(x12)+δn(x′12) for all x12,x′12∈M12.
Proof. Thanks to inductive hypothesis Cs for all 1≤s<m and relations (−x12−p1)(p2+x′12)p1p2⋯p2⏟n−3 copies=0, we have
δm(x12+x′12)=δm(Pn((−x12−p1),(p2+x′12),p1,p2,⋯,p2⏟n−3 copies))=∑i1+⋯+in=mPn(δi1(−x12−p1),δi2(p2+x′12),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies)=∑i1+⋯+in=mPn(δi1(−x12)+δi1(−p1),δi2(p2)+δi2(x′12),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies)=∑i1+⋯+in=mPn(δi1(−x12),δi2(p2),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies)+∑i1+⋯+in=mPn(δi1(−x12),δi2(x′12),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies)+∑i1+⋯+in=mPn(δi1(−p1),δi2(p2),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies)+∑i1+⋯+in=mPn(δi1(−p1),δi2(x′12),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies)=δm(Pn(−x12,p2,p1,p2,⋯,p2⏟n−3 copies))+δm(Pn(−x12,x′12,p1,p2,⋯,p2⏟n−3 copies))+δm(Pn(−p1,p2,p1,p2,⋯,p2⏟n−3 copies))+δm(Pn(−p1,x′12,p1,p2,⋯,p2⏟n−3 copies))=δm(x12)+δm(x′12). |
That is, δm(x12+x′12)=δm(x12)+δm(x′12) for all x12,x′12∈A12.
Lemma 4.4. With notations as above, we have
1)δm(a11+a′11)−δm(a11)−δm(a′11)∈Z(T);
2)δm(a22+a′22)−δm(a22)−δm(a′22)∈Z(T)
for all aii,a′ii∈Aii with i∈{1,2}.
Proof. We only prove the statement 1). The statement 2) can be proved in a similar way. Because of relations x12p1(a11+a′11)p2⋯p2⏟n−3 copies=x12p1a11p2⋯p2⏟n−3 copies=0=x12p1a′11p2⋯p2⏟n−3 copies, we arrive at
δm((a11+a′11)x12)=δm(Pn(x12,p1,(a11+a′11),p2,⋯,p2⏟n−3 copies))=∑i1+⋯+in=mPn(δi1(x12),δi2(p1),δi3(a11+a′11),δi4(p2),⋯,δin(p2)⏟n−3 copies). |
On the other hand, we have
δm((a11+a′11)x12)=δm(Pn(x12,p1,(a11),p2,⋯,p2⏟n−3 copies))+δm(Pn(x12,p1,(a′11),p2,⋯,p2⏟n−3 copies))=∑i1+⋯+in=mPn(δi1(x12),δi2(p1),δi3(a11),δi4(p2),⋯,δin(p2)⏟n−3 copies)+∑i1+⋯+in=mPn(δi1(x12),δi2(p1),δi3(a′11),δi4(p2),⋯,δin(p2)⏟n−3 copies)=∑i1+⋯+in=mPn(δi1(x12),δi2(p1),δi3(a11)+δi3(a′11),δi4(p2),⋯,δin(p2)⏟n−3 copies) |
for all a11∈A11,x12∈A12. On comparing the above two relations together with inductive hypothesis Cs for all 1≤s<m, we see that
0=∑i1+⋯+in=mPn(δi1(x12),δi2(p1),δi3(a11+a′11)−(δi3(a11)+δi3(a′11)),δi4(p2),⋯,δin(p2)⏟n−3 copies)=∑i1+⋯+in=m,i3≠mPn(δi1(x12),δi2(p1),δi3(a11+a′11)−(δi3(a11)+δi3(a′11)),δi4(p2),⋯,δin(p2)⏟n−3 copies)+Pn(x12,p1,δm(a11+a′11)−(δm(a11)+δm(a′11)),p2,⋯,p2⏟n−3 copies)=Pn(x12,p1,δm(a11+a′11)−(δm(a11)+δm(a′11)),p2,⋯,p2⏟n−3 copies), |
which is
p1(δm(a11+a′11)−(δm(a11)+δm(a′11)))x12=x12(δm(a11+a′11)−(δm(a11)+δm(a′11)))p2. | (4.2) |
It follows from the center of triangular algebra T and the above equation that
p1(δm(a11+a′11)−(δm(a11)+δm(a′11)))p1⊕p2(δm(a11+a′11)−(δm(a11)+δn(a′11)))p2∈Z(T). | (4.3) |
In the following, we prove
p1(δm(a11+a′11)−(δm(a11)+δm(a′11)))p2=0 |
for all a11,a′11∈A11.
Benefitting from (a11+a′11)p2⋯p2⏟n−1 copies=a11p2⋯p2⏟n−1 copies=a′11p2⋯p2⏟n−1 copies=0, we have
0=δm(Pn((a11+a′11),p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(a11+a′11),δi2(p2),δi3(p2),⋯,δin(p2)⏟n−2 copies) |
and
0=δm(Pn(a11,p2,⋯,p2))+δm(Pn(a′11,p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(a11),δi2(p2),δi3(p2),⋯,δin(p2)⏟n−2 copies)+∑i1+⋯+in=mPn(δi1(a′11),δi2(p2),δi3(p2),⋯,δin(p2)⏟n−2 copies)=∑i1+⋯+in=mPn(δi1(a11)+δi1(a′11),δi2(p2),δi3(p2),⋯,δin(p2)⏟n−2 copies). |
By combining the above two equations with inductive hypothesis Cs for all 1≤s<m, we can get
0=∑i1+⋯+in=mPn(δi1(a11+a′11)−(δi1(a′11)+δi1(a′11)),δi2(p2),δi3(p2),⋯,δin(p2)⏟n−2 copies)=∑i1+⋯+in=m,i1≠mPn(δi1(δi1(a11+a′11)−(δi1(a′11)+δi1(a′11)),δi2(p2),δi3(p2),⋯,δin(p2)⏟n−2 copies)+Pn(δm(a11+a′11)−(δm(a′11)+δm(a′11)),p2,p2,⋯,p2⏟n−2 copies)=Pn(δm(a11+a′11)−(δm(a′11)+δm(a′11)),p2,p2,⋯,p2⏟n−2 copies), |
which is
\begin{align} p_1(\delta_m(a_{11}+a_{11}^\prime)-(\delta_m(a_{11})+\delta_m(a_{11}^\prime)))p_2 = 0. \end{align} | (4.4) |
Combining (4.5) and (4.6) , this claim holds.
Lemma 4.5. With notations as above, we have \delta_m(a_{11}+x_{12}+b_{22})-\delta_m(a_{11})-\delta_m(x_{12})-\delta_m(b_{22})\in \mathcal{Z}(\mathcal{T}) for all a_{11}\in A_{11}, x_{12}\in A_{12}, a_{22}\in A_{22} .
Proof. For arbitrary a_{11}\in A_{11}, x_{12}\in A_{12}, a_{22}\in A_{22} , in view of (a_{11}+x_{12}+b_{22})x_{12}^\prime p_1p_2\cdots p_2 = 0 , we have
\begin{aligned} \delta_m(x_{12^\prime}b_{22}-a_{11}x_{12}^\prime)& = \delta_m(P_n(a_{11}+x_{12}+b_{22}, x_{12}^\prime, p_1, p_2, \cdots , p_2))\\ & = \sum\limits_{i_1+\cdots +i_n = m}P_n(\delta_{i_1}(a_{11}+x_{12}+b_{22}), \delta_{i_2}(x_{12}^\prime), \delta_{i_3}(p_1), \underbrace{\delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2)}_{n-3 \ \text{copies}}) \end{aligned} |
and
\begin{aligned} &\delta_m(x_{12}^\prime b_{22}-a_{11}x_{12}^\prime) = \delta_m(x_{12}^\prime b_{22})+\delta_m(-a_{11}x_{12}^\prime)\\ & = \delta_m(P_n(a_{11}, x_{12}^\prime, p_1, p_2, \cdots , p_2))+\delta_m(P_n(x_{12}, x_{12}^\prime, p_1, p_2, \cdots , p_2))\\ &+\delta_m(P_n(b_{22}, x_{12}^\prime, p_1, p_2, \cdots , p_2))\\ & = \sum\limits_{i_1+\cdots +i_n = m}P_n(\delta_{i_1}(a_{11})+\delta_{i_1}(x_{12})+\delta_{i_1}(b_{22}), \delta_{i_2}(x_{12}^\prime), \delta_{i_3}(p_1), \underbrace{\delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2)}_{n-3 \ \text{copies}}). \end{aligned} |
Let us set W_i = \delta_i(a_{11}+x_{12}+b_{22})-(\delta_i(a_{11})+\delta_i(x_{12})+\delta_i(b_{22})) . Taking into accounts the above two equations and using inductive hypothesis \mathfrak{C}_s for all 1\leq s\leq n , we have
\begin{aligned} 0& = \sum\limits_{i_1+\cdots +i_n = m}P_n(W_{i_1}, \delta_{i_2}(x_{12}^\prime), \delta_{i_3}(p_1), \underbrace{\delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2)}_{n-3 \ \text{copies}})\\ & = \sum\limits_{i_1+\cdots +i_n = m, i_1\neq m}P_n(W_{i_1}, \delta_{i_2}(x_{12}^\prime), \delta_{i_3}(p_1), \underbrace{\delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2)}_{n-3 \ \text{copies}})\\ &+P_n(W_m, x_{12}^\prime, p_1, \underbrace{p_2, \cdots , p_2}_{n-3 \ \text{copies}})\\ & = P_n(W_m, x_{12}^\prime, p_1, \underbrace{p_2, \cdots , p_2}_{n-3 \ \text{copies}}), \end{aligned} |
which is p_1W_mx_{12}^\prime-x_{12}^\prime W_mp_2 = 0 , i.e.,
\begin{align} p_1W_mp_1\oplus p_2W_mp_2\in \mathcal{Z}(\mathcal{T}). \end{align} | (4.5) |
In the following part, we prove p_1W_mp_2 = 0 . It is clear that (a_{11}+x_{12}+b_{22})(-p_1) \underbrace{p_2\cdots p_2}_{n-2 \ \text{copies}} = 0 , then
\begin{aligned} \delta_m(x_{12})& = \delta_m(P_n(a_{11}+x_{12}+b_{22}, -p_1, \underbrace{p_2, \cdots, p_2}_{n-2\ \text{copies}})\\ & = \sum\limits_{i_1+\cdots +i_n = m}P_n(\delta_{i_1}(a_{11}+x_{12}+b_{22}), \delta_{i_2}(-p_1), \underbrace{\delta_{i_3}(p_2), \cdots , \delta_{i_n}(p_2)}_{n-2 \ \text{copies}})\\ \end{aligned} |
and
\begin{aligned} \delta_n(x_{12})& = \delta_m(P_n(a_{11}, -p_1, \underbrace{p_2, \cdots, p_2}_{n-2\ \text{copies}})+\delta_m(P_n(x_{12}, -p_1, \underbrace{p_2, \cdots, p_2}_{n-2\ \text{copies}})\\ &+\delta_m(P_n(b_{22}, -p_1, \underbrace{p_2, \cdots, p_2}_{n-2\ \text{copies}})\\ & = \sum\limits_{i_1+\cdots +i_n = m}P_n(\delta_{i_1}(a_{11})+\delta_{i_1}(x_{12})+\delta_{i_1}(b_{22}), \delta_{i_2}(-p_1), \underbrace{\delta_{i_3}(p_2), \cdots , \delta_{i_n}(p_2)}_{n-2 \ \text{copies}}). \end{aligned} |
According to the above two equations and inductive hypothesis \mathfrak{C}_s for all 1\leq s\leq m , we can get
\begin{aligned} 0& = \sum\limits_{i_1+\cdots +i_n = m}P_n(W_{i_1}, \delta_{i_2}(-p_1), \underbrace{\delta_{i_3}(p_2), \cdots , \delta_{i_n}(p_2)}_{n-2 \ \text{copies}})\\ & = \sum\limits_{i_1+\cdots +i_n = m, i_1\neq m}P_n(W_{i_1}, \delta_{i_2}(-p_1), \underbrace{\delta_{i_3}(p_2), \cdots , \delta_{i_n}(p_2)}_{n-2 \ \text{copies}})+P_n(W_m, -p_1, \underbrace{p_2, \cdots , p_2}_{n-2 \ \text{copies}})\\ & = P_n(W_m, -p_1, \underbrace{p_2, \cdots , p_2}_{n-2 \ \text{copies}}), \end{aligned} |
which is
\begin{align} p_1W_mp_2 = 0. \end{align} | (4.6) |
It follows from relations (4.7)–(4.8) that this lemma holds.
Next, we give the proof of this theorem. For arbitrary x = a_{11}+x_{12}+b_{22} and y = a_{11}^\prime+x_{12}^\prime+b_{22}^\prime , we have
\begin{aligned} \delta_m(x+y)& = \delta_m(a_{11}+a_{11}^\prime+x_{12}+x_{12}^\prime+b_{22}+b_{22}^\prime)\\ & = \delta_m(a_{11}+a_{11}^\prime)+\delta_m(x_{12}+x_{12}^\prime)+\delta_m(b_{22}+b_{22}^\prime)+Z_1\\ & = \delta_m(a_{11})+\delta_m(a_{11}^\prime)+\delta_m(x_{12})+\delta_m(x_{12}^\prime)+\delta_m(b_{22})+\delta_m(b_{22}^\prime)+Z_1+Z_2+Z_3\\ & = \delta_m(x)+\delta_m(y)+Z_1+Z_2+Z_3+Z_4+Z_5, \end{aligned} |
which implies that \delta_m(x+y)-\delta_m(x)-\delta_m(y)\in \mathcal{Z}(\mathcal{T}) .
Based on the additive of \delta_m on \mathcal{T} , we give the main result in this section reading as follows.
Theorem 4.2. Let \mathcal{T} = \left[\begin{array}{cc} A_{11} & A_{12}\\ O & A_{22} \end{array}\right] be a triangular algebra satisfying
\text{i}) \pi_{A_{11}}(\mathcal{Z}(\mathcal{T})) = \mathcal{Z}(\mathcal{A}_{11}) and \pi_{A_{22}}(\mathcal{Z}(\mathcal{T})) = \mathcal{Z}(\mathcal{A}_{22}) ;
\text{ii}) For any a_{11}\in A_{11} , if [a_{11}, A_{11}]\in \mathcal{Z}(\mathcal{A}_{11}) , then a_{11}\in \mathcal{Z}(\mathcal{A}_{11}) , or for any a_{22}\in A_{22} , if [a_{22}, A_{22}]\in \mathcal{Z}(\mathcal{A}_{22}) , then a_{22}\in \mathcal{Z}(\mathcal{A}_{22}) .
Suppose that a sequence \Delta = \{\delta_m\}_{m\in \mathcal{N}} of mappings \delta_m:\mathcal{T}\rightarrow \mathcal{T} is a nonlinear map satisfying
\delta_m(P_n(x_1, x_2, \cdots, x_n)) = \sum\limits_{i_1+\cdots +i_n = m}P_n(\delta_{i_1}(x_1), \delta_{i_2}(x_2), \cdots, \delta_{i_n}(x_n)) |
for all x_1, x_2, \cdots, x_n \in \mathcal{T} with x_1x_2\cdots x_n = 0 and n\geq 3 . For every m\in \mathcal{N} ,
\delta_m(x) = \chi_m(x)+f_m(x) |
for all x\in \mathcal{T} , where a sequence \Upsilon = \{\chi_m \}_{m\in \mathcal{N}} of additive mapping \chi_m:\mathcal{T}\rightarrow \mathcal{T} is a higher derivation, and f_m:\mathcal{T}\rightarrow \mathcal{Z}(\mathcal{T}) is a nonlinear mapping such that f_m(P_n(x_1, x_2, \cdots, x_n)) = 0 for any x_1, x_2, \cdots, x_n \in \mathcal{T} with x_1x_2\cdots x_n = 0 .
In the process of proof, we will use mathematical induction for index m . For m = 1 , \delta_1 = L_n is a Lie-n derivation on \mathcal{T} by local action at zero. By Theorem 3.2, it follows from Theorem 3.2 that there exists an additive derivation d_1 and a nonlinear center mapping f_1 , satisfying f_1(P_n(x_1, x_2, \cdots, x_n)) = 0 for any x_1, x_2, \cdots, x_n \in \mathcal{T} with x_1x_2\cdots x_n = 0 and n\geq 3 , such that \delta_1(x) = d_1(x)+f_1(x) for all x\in \mathcal{T} . Furthermore, \delta_1 and d_1 satisfy the following properties
\mathfrak{F}_1 = \begin{cases} \delta_1(0) = 0, \delta_1(A_{11})\subseteq A_{11}+A_{12}+\mathcal{Z}(\mathcal{T}), \delta_1(A_{22})\subseteq A_{22}+A_{12}+\mathcal{Z}(\mathcal{T});\\ \delta_1(A_{12})\subseteq A_{12}, \delta_1(p_i)\subseteq A_{12}+\mathcal{Z}(\mathcal{T});\\ d_1(A_{ii})\subseteq A_{ii}+A_{ij}, d_1(A_{12})\subseteq A_{12}; f_1(P_n(x_1, x_2, \cdots, x_n)) = 0 \end{cases} |
for i\leq j\in \{1, 2\} and for any x_1, \cdots, x_n\in \mathcal{T} with x_1\cdots x_n = 0 .
We assume that the result holds for s for all 1 < s < m , m\in \mathcal{N} , then there exists an additive derivation d_s and a nonlinear center mapping f_s , satisfying f_s(P_n(x_1, x_2, \cdots, x_n)) = 0 for any x_1, x_2, \cdots, x_n \in \mathcal{T} with x_1x_2\cdots x_n = 0 , such that \delta_s(x) = d_s(x)+f_s(x) for all x\in \mathcal{T} . Moreover, \delta_s and d_s satisfy the following properties
\mathfrak{F}_s = \begin{cases} \delta_s(0) = 0, \delta_1(A_{11})\subseteq A_{11}+A_{12}+\mathcal{Z}(\mathcal{T}), \delta_1(A_{22})\subseteq A_{22}+A_{12}+\mathcal{Z}(\mathcal{T});\\ \delta_s(A_{12})\subseteq A_{12}, \delta_s(p_i)\subseteq A_{12}+\mathcal{Z}(\mathcal{T});\\ d_s(A_{ii})\subseteq A_{ii}+A_{ij}, d_s(A_{12})\subseteq A_{12};f_s(P_n(x_1, x_2, \cdots, x_n)) = 0 \end{cases} |
for i\leq j\in \{1, 2\} and for any x_1, x_2, \cdots, x_n \in \mathcal{T} with x_1x_2\cdots x_n = 0 .
The induction process can be realized through a series of lemmas.
Lemma 4.6. With notations as above, we have
1) \delta_m(A_{12})\subseteq A_{12} ;
2) p_1\delta_m(p_1)p_1\oplus p_2\delta_m(p_1)p_2\in \mathcal{Z}(\mathcal{T}) and p_1\delta_m(p_2)p_1\oplus p_2\delta_m(p_2)p_2\in \mathcal{Z}(\mathcal{T}) ;
3) \delta_m(p_1)\in M_{12}+\mathcal{Z}(\mathcal{T}) .
Proof. Because of x_{12}p_1p_1\underbrace{p_2\cdots p_2}_{n-3 \ \text{copies}} = 0 for x_{12}\in A_{12} , with the help of condition \mathfrak{F}_s for all 1 < s < m , we have
\begin{aligned} \delta_m(x_{12})& = \delta_m(P_n(x_{12}, p_1, p_1, p_2, \cdots , p_2))\\ & = \sum\limits_{i_1+\cdots+i_n = m}P_n(\delta_{i_1}(x_{12}), \delta_{i_2}(p_1), \delta_{i_3}(p_1), \delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2))\\ & = \sum\limits_{i_1+\cdots+i_n = m, 0 < i_1, \cdots, i_n < m}P_n(\delta_{i_1}(x_{12}), \delta_{i_2}(p_1), \delta_{i_3}(p_1), \delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2))\\ &+P_n(\delta_m(x_{12}), p_1, p_1, p_2, \cdots , p_2)+P_n(x_{12}, \delta_m(p_1), p_1, p_2, \cdots , p_2)\\ &+P_n(x_{12}, p_1, \delta_m(p_1), p_2, \cdots , p_2)+\sum\limits_{s = 4}^nP_n(x_{12}, p_1, p_1, p_2, \cdots , p_2, \underbrace{\delta_m(p_2)}_{s-th \ component}, \cdots , p_2)\\ & = P_n(\delta_m(x_{12}), p_1, p_1, p_2, \cdots , p_2)+P_n(x_{12}, \delta_m(p_1), p_1, p_2, \cdots , p_2)\\ &+P_n(x_{12}, p_1, \delta_m(p_1), p_2, \cdots , p_2)\\ & = p_1\delta_m(x_{12})p_2+p_1\delta_m(p_1)x_{12}+\delta_m(p_1)x_{12}-2x_{12}\delta_m(p_1), \end{aligned} |
then we can obtain that \delta_m(x_{12})\in A_{12} . Multiplying by p_1 on the left side and p_2 on the right side of the above equation, we can obtain that p_1\delta_m(p_1)x_{12} = x_{12}\delta_m(p_1)p_2 for all x_{12}\in A_{12} . It follows from definition of center that
p_1\delta_m(p_1)p_1\oplus p_2\delta_m(p_1)p_2\in \mathcal{Z}(\mathcal{T}). |
Because of p_2x_{12}p_1p_2\cdots p_2 = 0 , we adopt the same discussion as relations
\begin{aligned} \delta_m(x_{12})& = \delta_m(P_n(p_2, x_{12}, p_1, p_2\cdots, p_2))\\ & = \sum\limits_{i_1+\cdots+i_n = m}P_n(\delta_{i_1}(p_{2}), \delta_{i_2}(x_{12}), \delta_{i_3}(p_1), \delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2))\\ & = \sum\limits_{i_1+\cdots+i_n = m, 0 < i_1, \cdots, i_n < m}P_n(\delta_{i_1}(p_{2}), \delta_{i_2}(x_{12}), \delta_{i_3}(p_1), \delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2))\\ &+P_n(\delta_m(p_{2}), x_{12}, p_1, p_2, \cdots , p_2)+P_n(p_2, \delta_m(x_{12}), p_1, p_2, \cdots , p_2)\\ &+P_n(p_2, x_{12}, \delta_m(p_1), p_2, \cdots , p_2)+\sum\limits_{s = 4}^nP_n(p_2, x_{12}, p_1, p_2, \cdots , p_2, \underbrace{\delta_m(p_2)}_{s-th \ component}, \cdots , p_2)\\ & = P_n(\delta_m(p_2), x_{12}, p_1, p_2, \cdots , p_2)+P_n(p_2, \delta_m(x_{12}), p_1, p_2, \cdots , p_2)\\ &+P_n(p_2, x_{12}, \delta_m(p_1), p_2, \cdots , p_2)\\ & = -p_1\delta_m(p_2)x_{12}+x_{12}\delta_m(p_2)p_2+p_1\delta_m(x_{12})p_2-x_{12}\delta_m(p_1)p_2+\delta_m(p_1)x_{12}\\ & = -p_1\delta_m(p_2)x_{12}+x_{12}\delta_m(p_2)p_2+p_1\delta_m(x_{12})p_2 \end{aligned} |
Multiplying by p_1 on the left side and p_2 on the right side of the above equation, we can obtain that p_1\delta_m(p_2)x_{12} = x_{12}\delta_m(p_2)p_2 for all x_{12}\in A_{12} . It follows from definition of center and we can prove that p_1\delta_m(p_2)p_1\oplus p_2\delta_m(p_2)p_2\in \mathcal{Z}(\mathcal{T}) holds.
Lemma 4.7. With notations as above, we have
1) \delta_m(a_{11})\in A_{11}+A_{12}+\mathcal{Z}(\mathcal{T}) , where p_2\delta_m(a_{11})p_2\in \mathcal{Z}(A_{11}) ;
2) \delta_m(a_{22})\in A_{22}+A_{12}+\mathcal{Z}(\mathcal{T}) , where p_1\delta_m(a_{22})p_1\in \mathcal{Z}(A_{22})
for all a_{ii}\in A_{ii} with i\in \{1, 2\} .
Proof. In fact, it is clear that a_{22}a_{11}a_{12}\underbrace{p_2\cdots p_2}_{n-3 \ \text{copies}} = 0 for all a_{ij}\in A_{ij} and for all i, j \in \{1, 2\} , then according to inductive hypothesis \mathfrak{F}_s , we have
\begin{aligned} 0 = &\delta_m(P_n(a_{22}, a_{11}, a_{12}, p_2, \cdots , p_2))\\ = &\sum\limits_{i_1+\cdots +i_n = m}P_n(\delta_{i_1}(a_{22}), \delta_{i_2}(a_{11}), \delta_{i_3}(a_{12}), \delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2))\\ = &\sum\limits_{i_1+\cdots +i_n = m, i_1, \cdots , i_n < m}P_n(\delta_{i_1}(a_{22}), \delta_{i_2}(a_{11}), \delta_{i_3}(a_{12}), \delta_{i_4}(p_2), \cdots , \delta_{i_n}(p_2))\\ &+P_n(\delta_m(a_{22}), a_{11}, a_{12}, p_2, \cdots , p_2)+P_n(a_{22}, \delta_m(a_{11}), a_{12}, p_2, \cdots , p_2)\\ = &P_n(\delta_m(a_{22}), a_{11}, a_{12}, p_2, \cdots , p_2)+P_n(a_{22}, \delta_m(a_{11}), a_{12}, p_2, \cdots , p_2)\\ = &P_n(p_1\delta_m(a_{22})p_1, a_{11}, a_{12}, p_2, \cdots , p_2)+P_n(a_{22}, p_2\delta_m(a_{11})p_2, a_{12}, p_2, \cdots , p_2)\\ = &P_{n-1}([p_1\delta_m(a_{22})p_1, a_{11}]+[a_{22}, p_2\delta_m(a_{11})p_2], a_{12}, p_2, \cdots , p_2) \end{aligned} |
for all a_{ij}\in A_{ij} and for all i\leq j \in \{1, 2\} . In light of Lemma 3.1, we obtain
\begin{align} [p_1\delta_m(a_{22})p_1, a_{11}]\oplus [a_{22}, p_2\delta_m(a_{11})p_2]\in \mathcal{Z}(\mathcal{T}) \end{align} | (4.7) |
for all a_{ii}\in A_{ii} and or all i \in \{1, 2\} . With the help of characterization of algebraic center, we have
[p_1\delta_m(a_{22})p_1, a_{11}]\in \mathcal{Z}(A_{11}) \ \text{and} \ [a_{22}, p_2\delta_m(a_{11})p_2]\in \mathcal{Z}(A_{22}), |
then
\begin{align} p_1\delta_m(a_{22})p_1\in \mathcal{Z}(A_{11}) \ \text{and} \ p_2\delta_m(a_{11})p_2\in \mathcal{Z}(A_{22}) \end{align} | (4.8) |
for all a_{ii}\in A_{ii} and for all i \in \{1, 2\} . Further based on theorem hypothesis (\text{ii}) and above Eqs (4.9) and (4.10) , we arrive at
\begin{aligned} \delta_m(a_{11})& = p_1\delta_m(a_{11})p_1-\tau^{-1}(p_2\delta_m(a_{11})p_2)+p_1\delta_m(a_{11})p_2\\ &+\tau^{-1}(p_2\delta_m(a_{11})p_2)+p_2\delta_m(a_{11})p_2\in A_{11}+A_{12}+\mathcal{Z}(\mathcal{T}) \end{aligned} |
and
\begin{aligned} \delta_m(a_{22})& = p_2\delta_m(a_{22})p_2-\tau(p_1\delta_m(a_{22})p_1)+p_1\delta_m(a_{22})p_2\\ &+p_1\delta_m(a_{22})p_1+\tau(p_1\delta_m(a_{22})p_1)\in A_{22}+A_{12}+\mathcal{Z}(\mathcal{T}) \end{aligned} |
for all a_{ij}\in A_{ij} with i\leq j\in \{1, 2\} . We can conclude that this claim can be established.
Now, we define mapping f_{m1}(a_{11}) = \tau^{-1}(p_2\delta_m(a_{11})p_2)+p_2\delta_m(a_{11})p_2 and f_{m2}(a_{22}) = p_1\delta_m(a_{22})p_1+\tau(p_1\delta_m(a_{22})p_1) for all a_{11}\in A_{11} and a_{22}\in A_{22} . It follows from Lemma 4.7 that f_{m1}:A_{11}\rightarrow \mathcal{Z}(A_{11}) such that f_{n1}(P_n(a_{11}^1, \cdots, a_{11}^n)) = 0 for all a_{11}^1, \cdots, a_{11}^n\in A_{11} with a_{11}^1a_{11}^2\cdots a_{11}^n = 0 and f_{m2}:A_{22}\rightarrow \mathcal{Z}(A_{22}) , such that f_{m2}(P_n(a_{22}^1, \cdots, a_{22}^n)) = 0 for all a_{22}^1, \cdots, a_{22}^n\in A_{22} with a_{22}^1a_{22}^2\cdots a_{22}^n = 0 . Now, set
\begin{align} \begin{aligned} f_m(x)& = f_{m1}(a_{11})+f_{m2}(a_{22}) = \tau^{-1}(p_2\delta_m(a_{11})p_2)+p_2\delta_m(a_{11})p_2\\ &+p_1\delta_m(a_{22})p_1+\tau(p_1\delta_m(a_{22})p_1)\\ \end{aligned} \end{align} | (4.9) |
for all x = a_{11}+a_{12}+a_{22}\in \mathcal{T} . It is clear that f_m(x)\in \mathcal{Z}(\mathcal{T}) and f_m(P_n(x_1, x_2, \cdots, x_n)) = 0 with x_1x_2\cdots x_n = 0 for all x_1, x_2, \cdots, x_n\in \mathcal{T} . Define a new mapping
\begin{align} \varpi_m(x) = \delta_m(x)-f_m(x) \end{align} | (4.10) |
for all x\in \mathcal{T} .
Taking into account Lemmas 4.6 and 4.7 together with (4.11) and (4.12) , we can easily get the following Lemma 4.8.
Lemma 4.8. With notations as above, we have
1) \varpi_m(0) = 0 , \varpi_m(a_{12}) = \delta_m(a_{12})\in A_{12} , \varpi_m(p_i)\in A_{12} ;
2) \varpi_m(a_{11})\in A_{11}+A_{12} and \varpi_m(a_{22})\in A_{22}+A_{12} ,
for all a_{ij}\in A_{ij} with i\leq j\in \{1, 2\} .
Lemma 4.9. With notations as above, we have
1) \varpi_m(a_{11}a_{12}) = a_{11}\varpi_m(a_{12})+\varpi_m(a_{11})a_{12}+\sum_{i+j = m, 0 < i, j < m}d_i(a_{11})d_{j}(a_{12}) ;
2) \varpi_m(a_{12}a_{22}) = a_{12}\varpi_m(a_{22})+\varpi_m(a_{12})a_{22}+\sum_{i+j = n, 0 < i, j < m}d_i(a_{12})d_{j}(a_{22})
for all a_{ij}\in A_{ij} with i\leq j\in \{1, 2\} .
Proof. Now, we only prove the conclusion 1) , and conclusion 2) can be proved by similar methods. It follows from a_{12}a_{11}p_1\underbrace{p_2\cdots p_2}_{n-3 \ \text{copies}} = 0 and the induction hypothesis \mathfrak{F}_s for all 1\leq s\leq m-1 that
\begin{aligned} \varpi_m(a_{11}a_{12})& = \delta_m(a_{11}a_{12}) = \delta_m(P_n(a_{12}, a_{11}, p_1, p_2, \cdots, p_2))\\ & = \sum\limits_{i_1+\cdots +i_n = m}P_n(\delta_{i_1}(a_{12}), \delta_{i_2}(a_{11}), \delta_{i_3}(p_1), \delta_{i_4}(p_2), \cdots, \delta_{i_n}(p_2))\\ & = \sum\limits_{i_1+\cdots +i_n = m, i_1, \cdots , i_n < m}P_n(\delta_{i_1}(a_{12}), \delta_{i_2}(a_{11}), \delta_{i_3}(p_1), \delta_{i_4}(p_2), \cdots, \delta_{i_n}(p_2))\\ &+P_n(\delta_m(a_{12}), a_{11}, p_1, p_2, \cdots, p_2)+P_n(a_{12}, \delta_m(a_{11}), p_1, p_2, \cdots, p_2)\\ &+P_n(a_{12}, a_{11}, \delta_m(p_1), p_2, \cdots, p_2)\\ & = \sum\limits_{i_1+\cdots +i_n = m, i_1, \cdots , i_n < m}P_n(d_{i_1}(a_{12}), d_{i_2}(a_{11}), d_{i_3}(p_1), d_{i_4}(p_2), \cdots, d_{i_n}(p_2))\\ &+a_{11}\varpi_n(a_{12})+\varpi_n(a_{11})a_{12}\\ & = \sum\limits_{i_1+i_2 = m, 0 < i_1, i_2 < m}P_n(d_{i_1}(a_{12}), d_{i_2}(a_{11}), p_1, p_2, \cdots, p_2) +a_{11}\varpi_n(a_{12})+\varpi_n(a_{11})a_{12}\\ & = a_{11}\varpi_n(a_{12})+\varpi_n(a_{11})a_{12}+\sum\limits_{i_1+i_2 = m, 0 < i_1, i_2 < m}d_{i_2}(a_{11})d_{i_1}(a_{12})\\ \end{aligned} |
for all a_{st}\in A_{st} with s\leq t\in \{1, 2\} .
Adopt the same discussion as relations \varpi_m(a_{12}a_{22}) = \delta_m(a_{12}a_{22}) = \delta_m(P_n(a_{22}, a_{12}, p_1, p_2, \cdots, p_2)) with a_{22}a_{12}p_1p_2\cdots p_2 = 0 , and we can prove
\varpi_n(a_{12}a_{22}) = a_{12}\varpi_n(a_{22})+\varpi_n(a_{12})a_{22}+\sum\limits_{i+j = n, 0 < i, j < n}d_i(a_{12})d_{j}(a_{22}) |
for all a_{st}\in A_{st} with s\leq t\in \{1, 2\} .
Lemma 4.10. With notations as above, we have
1) \varpi_m(a_{11}a^\prime_{11}) = \varpi_m(a_{11})a^\prime_{11}+a_{11}\varpi_m(a^\prime_{11})p_2+\sum_{i+j = m, 0 < i, j < m}d_i(a_{11})d_{j}(a^\prime_{11}) ;
2) \varpi_m(b_{22}b^\prime_{22}) = \varpi_m(b_{22})b^\prime_{22}+b_{22}\varpi_m(b^\prime_{22})p_2+\sum_{i+j = n, 0 < i, j < m}d_i(b_{22})d_{j}(b^\prime_{22})
for all a_{ii}, a_{ii}^\prime\in A_{ii} with i\in \{1, 2\} .
Proof. For conclusion 1) , arbitrary a_{11}, a_{11}^\prime\in A_{11} and a_{12}\in A_{12} and by conclusion 1) in Lemma 4.9, we have
\begin{align} \begin{aligned} \varpi_m(a_{11}a_{11}^\prime a_{12})& = a_{11}a_{11}^\prime\varpi_m(a_{12})+\varpi_m(a_{11}a_{11}^\prime)a_{12}\\ &+\sum\limits_{i+j = m, 0 < i, j < m}d_i(a_{11}a_{11}^\prime)d_{j}(a_{12})\\ & = a_{11}a_{11}^\prime\varpi_m(a_{12})+\varpi_m(a_{11}a_{11}^\prime)a_{12}\\ &+\sum\limits_{i+j = m, 0 < i, j < m}(\sum\limits_{i_1+i_2 = i, 0 < i < m}d_{i_1}(a_{11})d_{i_2}(a_{11}^\prime))d_{j}(a_{12})\\ & = a_{11}a_{11}^\prime\varpi_m(a_{12})+\varpi_m(a_{11}a_{11}^\prime)a_{12}\\ &+\sum\limits_{i_1+i_2+j = m, 0 < i_1, i_2, j < m}d_{i_1}(a_{11})d_{i_2}(a_{11}^\prime)d_{j}(a_{12}) \end{aligned} \end{align} | (4.11) |
and
\begin{align} \begin{aligned} \varpi_m(a_{11}a_{11}^\prime a_{12})& = a_{11}\varpi_m(a_{11}^\prime a_{12})+\varpi_m(a_{11})a_{11}^\prime a_{12}\\ &+\sum\limits_{i+j = m, 0 < i, j < m}d_i(a_{11})d_{j}(a_{11}^\prime a_{12})\\ & = a_{11}a^\prime_{11}\varpi_m(a_{12})+a_{11}\varpi_m(a^\prime_{11})a_{12}+\varpi_m(a_{11})a_{11}^\prime a_{12}\\ &+\sum\limits_{i+j = n, 0 < i, j < m}a_{11}d_i(a^\prime_{11})d_{j}(a_{12})+\sum\limits_{i+j = m, 0 < i, j < m}d_i(a_{11})d_{j}(a^\prime_{11} a_{12})\\ & = a_{11}a^\prime_{11}\varpi_m(a_{12})+a_{11}\varpi_m(a^\prime_{11})a_{12}+\varpi_m(a_{11})a^\prime_{11} a_{12}\\ &+\sum\limits_{i+j = m, 0 < i, j < m}a_{11}d_i(a^\prime_{11})d_{j}(a_{12})+\sum\limits_{i+j = m, 0 < i, j < m}d_i(a_{11})(\sum\limits_{j_1+j_2 = j, 0 < j < m}d_{j_1}(a^\prime_{11})d_{j_2}( a_{12}))\\ & = a_{11}a^\prime_{11}\varpi_m(a_{12})+a_{11}\varpi_m(a^\prime_{11})a_{12}+\varpi_m(a_{11})a_{11}^\prime a_{12}\\ &+\sum\limits_{i+j = m, 0 < i, j < m}a_{11}d_i(a^\prime_{11})d_{j}(a_{12})+\sum\limits_{i+j_1+j_2 = m, 0 < i, j_1, j_2 < m}d_i(a_{11})d_{j_1}(a^\prime_{11})d_{j_2}( a_{12})\\ & = a_{11}a^\prime_{11}\varpi_m(a_{12})+a_{11}\varpi_m(a^\prime_{11})a_{12}+\varpi_m(a_{11})a^\prime_{11} a_{12}\\ &+\sum\limits_{i+j = m, 0 < i, j < m}d_i(a_{11})d_{j}(a^\prime_{11})a_{12}+\sum\limits_{i+j_1+j_2 = m, 0 < i, j_1, j_2 < m}d_i(a_{11})d_{j_1}(a^\prime_{11})d_{j_2}(a_{12}) \end{aligned} \end{align} | (4.12) |
for all a_{tt}, a_{tt}^\prime\in A_{tt} with t\in \{1, 2\} .
Combining (4.12) with (4.13) leads to
\varpi_m(a_{11}a_{11}^\prime)a_{12} = (\varpi_m(a_{11})a_{11}^\prime +a_{11}\varpi_m(a_{11}^\prime)+\sum\limits_{i+j = m, 0 < i, j < m}d_i(a_{11})d_{j}(a_{11}^\prime))a_{12} |
for all a_{tt}, a_{tt}^\prime\in A_{tt} with t\in \{1, 2\} .
Since \varpi_m(A_{11})\subseteq A_{11}+A_{12} and A_{12} are faithful as a left A_{11} -module, the above relation implies that
\begin{align} \varpi_m(a_{11}a_{11}^\prime)p_1 = \{\varpi_m(a_{11})a_{11}^\prime +a_{11}\varpi_m(a_{11}^\prime)+\sum\limits_{i+j = m, 0 < i, j < m}d_i(a_{11})d_{j}(a_{11}^\prime)\}p_1 \end{align} | (4.13) |
for all a_{11}, a_{11}^\prime\in A_{11} .
On the other hand, by a_{11}\underbrace{p_2\cdots p_2}_{n-1 \ \text{copies}} = 0 for all a_{11}\in A_{11} , we arrive at
\begin{aligned} 0& = \delta_m(P_n(a_{11}, \underbrace{p_2, \cdots , p_2}_{n-1 \ \text{copies}}))\\ & = P_n(\delta_m(a_{11}), \underbrace{p_2, \cdots , p_2}_{n-1 \ \text{copies}})+P_n(a_{11}, \delta_m(p_2), \underbrace{p_2, \cdots , p_2}_{n-2 \ \text{copies}})\\ &+\sum\limits_{i_1+\cdots+i_n = m, i_1, \cdots, i_n < m}P_n(\delta_{i_1}(a_{11}), \delta_{i_2}(p_2), \cdots , \delta_{i_n}(p_2))\\ & = P_n(\varpi_m(a_{11}), \underbrace{p_2, \cdots , p_2}_{n-1 \ \text{copies}})+P_n(a_{11}, \varpi_m(p_2), \underbrace{p_2, \cdots , p_2}_{n-2 \ \text{copies}})\\ &+\sum\limits_{i_1+\cdots+i_n = m, i_1, \cdots, i_n < m}P_n(d_{i_1}(a_{11}), d_{i_2}(p_2), \cdots , d_{i_n}(p_2))\\ \end{aligned} |
for all a_{11}, a_{11}^\prime\in A_{11} .
Since \varpi_n(A_{11})\subseteq A_{11}+A_{12}, \varpi_n(p_2)\in A_{12} and d_i(p_2)\in A_{12} , the above equation implies that
0 = \varpi_m(a_{11})p_2+a_{11}\varpi_m(p_2)+\sum\limits_{i+j = m, 0\leq i, j < m}d_i(a_{11})d_j(p_2) |
for all a_{11}, a_{11}^\prime\in A_{11} .
On substituting a_{11} by a_{11}a^\prime_{11} in above equation, we get
\begin{aligned} 0& = \varpi_m(a_{11}a^\prime_{11})p_2+a_{11}a^\prime_{11}\varpi_m(p_2)+\sum\limits_{i+j = m, 0\leq i, j < m}d_i(a_{11}a^\prime_{11})d_j(p_2)\\ & = \varpi_m(a_{11}a^\prime_{11})p_2+a_{11}a^\prime_{11}\varpi_m(p_2)\\ &+\sum\limits_{i+j = m, 0\leq i, j < m}(\sum\limits_{i_1+i_2 = i, 0\leq i_1, i_2 < m}d_{i_1}(a_{11})d_{i_2}(a^\prime_{11}))d_j(p_2)\\ & = \varpi_m(a_{11}a^\prime_{11})p_2+a_{11}a^\prime_{11}\varpi_m(p_2)\\ &+\sum\limits_{i_1+i_2+j = m, 0\leq i_1, i_2, j < m}d_{i_1}(a_{11})d_{i_2}(a^\prime_{11})d_j(p_2) \end{aligned} |
for all a_{11}, a_{11}^\prime\in A_{11} . Therefore, we have
\begin{align} \begin{aligned} &p_1(\varpi_m(a_{11}a^\prime_{11})p_2+a_{11}a^\prime_{11}\varpi_m(p_2)\\ &+\sum\limits_{i_1+i_2+j = m, 0\leq i_1, i_2, j < m}d_{i_1}(a_{11})d_{i_2}(a^\prime_{11})d_j(p_2))p_2 = 0. \end{aligned} \end{align} | (4.14) |
Again, note that a^\prime_{11} p_2\cdots p_2 = 0 for all a^\prime_{11}\in A_{11} , and we have
\begin{aligned} 0 = \delta_m(P_n(a^\prime_{11}, p_2, \cdots , p_2))\\ & = \sum\limits_{i_1+\cdots+i_n = m}P_n(\delta_{i_1}(a^\prime_{11}), \delta_{i_2}(p_2), \cdots , \delta_{i_n}(p_2))\\ & = P_n(\varpi_m(a^\prime_{11}), p_2, \cdots, p_2)]+P_n(a^\prime_{11}, \varpi_m(p_2), p_2, \cdots, p_2]\\ &+\sum\limits_{i_1+\cdots+i_n = m, i_1, \cdots, i_n < m}P_n(d_{i_1}(a^\prime_{11}), d_{i_2}(p_2), \cdots , d_{i_n}(p_2)). \end{aligned} |
This gives us
\begin{align} 0 = \varpi_m(a^\prime_{11})p_2+a^\prime_{11}\varpi_m(p_2)+\sum\limits_{i+j = m, 0\leq i, j < m}d_i(a^\prime_{11})d_j(p_2). \end{align} | (4.15) |
Now, left multiplying a_{11} in (4.16) and combining it with (4.15) gives us
\varpi_m(a_{11}a^\prime_{11})p_2+\sum\limits_{i+j+k = m, 0\leq i, 0 < j}d_i(a_{11})d_j(a^\prime_{11})d_k(p_2) = a_{11}\varpi_m(a^\prime_{11})p_2. |
This implies that
\varpi_m(a_{11}a^\prime_{11})p_2+\sum\limits_{i = 1}^md_i(a_{11})\sum\limits_{j+k = m-i, 0\leq i}d_j(a^\prime_{11})d_k(p_2) = a_{11}\varpi_m(a^\prime_{11})p_2. |
Now, using the condition \mathfrak{F}_s , we find that
\varpi_m(a_{11}a^\prime_{11})p_2-\sum\limits_{i = 1}^{m-1}d_i(a_{11})d_{m-i}(a^\prime_{11})p_2 = a_{11}\varpi_m(a^\prime_{11})p_2, |
which gives
\varpi_m(a_{11}a^\prime_{11})p_2 = a_{11}\varpi_m(a^\prime_{11})p_2+\sum\limits_{i = 1}^{m-1}d_i(a_{11})d_{m-i}(a^\prime_{11})p_2. |
Hence,
\begin{align} \varpi_m(a_{11}a^\prime_{11})p_2 = \{\varpi_m(a_{11})a^\prime_{11}+a_{11}\varpi_m(a^\prime_{11})p_2+\sum\limits_{i+j = m, 0 < i, j < m}d_i(a_{11})d_{m-i}(a^\prime_{11})\}p_2. \end{align} | (4.16) |
Now, adding (4.14) and (4.17) , we have
\varpi_m(a_{11}a^\prime_{11}) = \varpi_m(a_{11})a^\prime_{11}+a_{11}\varpi_m(a^\prime_{11})p_2+\sum\limits_{i+j = m, 0 < i, j < m}d_i(a_{11})d_{j}(a^\prime_{11}). |
Adopting the same discussion, we have
\varpi_m(b_{22}b^\prime_{22}) = \varpi_m(b_{22})b^\prime_{22}+b_{22}\varpi_m(b^\prime_{22})p_2+\sum\limits_{i+j = m, 0 < i, j < m}d_i(b_{22})d_{j}(b^\prime_{22}) |
for all b_{22}, b^\prime_{22}\in A_{22} .
Remark 4.1. Now, we establish a mapping g_m:\mathcal{T}\rightarrow \mathcal{Z}(\mathcal{T}) by
g_m(x) = \varpi_m(x)-\varpi_m(p_1xp_1)-\varpi_m(p_1xp_2)-\varpi_m(p_2xp_2) |
and g_m(P_n(x_1, \cdots, x_n)) = 0 with x_1\cdots x_n = 0 for all x_1, \cdots, x_n\in \mathcal{T} , then define a mapping \chi_m(x) = \varpi_m(x)-g_m(x) for all x\in \mathcal{T} . It is easy to verify that
\chi_m(a_{11}+a_{12}+a_{22}) = \chi_m(a_{11})+\chi_m(a_{12})+\chi_m(a_{22}). |
From the definition of \chi_m and g_m , we find that
\varphi_m(x) = \varpi_m(x)+f_m(x) = \chi_m(x)+g_m(x)+f_m(x) = \chi_m(x)+h_m(x), |
where h_m(x) = g_m(x)+f_m(x) for all x\in \mathcal{T} .
Lemma 4.11. With notations as above, we obtain that \{\chi_i\}^{i = m}_{i = 0} is an additive higher derivation on triangular algebras \mathcal{T} .
Proof. Suppose that x, y\in \mathcal{T} , such that x = a_{11}+a_{12}+a_{22} and y = a^\prime_{11}+a^\prime_{12}+a^\prime_{22} , where a_{ij}, a^\prime_{ij}\in A_{ij} with i\leqslant j\in\{1, 2\} , then
\begin{aligned} \chi_m(x+y)& = \chi_m((a_{11}+a_{12}+a_{22})+(a^\prime_{11}+a^\prime_{12}+a^\prime_{22}))\\ & = \chi_m((a_{11}+a^\prime_{11})+(a_{12}+a^\prime_{12})+(a_{22}+a^\prime_{22}))\\ & = \chi_m(a_{11}+a^\prime_{11})+\chi_m(a_{12}+a^\prime_{12})+\chi_m(a_{22}+a^\prime_{22})\\ & = \chi_m(a_{11})+\chi_m(a^\prime_{11})+\varpi_m(a_{12})+\chi_m(a^\prime_{12})+\chi_m(a_{22})+\chi_m(a^\prime_{22})\\ & = \chi_m(a_{11}+a_{12}+a_{22})+\chi_m(a^\prime_{11}+a^\prime_{12}+a^\prime_{22}))\\ & = \chi_m(x)+\chi_m(y). \end{aligned} |
By Lemmas 4.8 and 4.10, we have
\begin{align} \begin{aligned} \chi_m(xy)& = \chi_m((a_{11}+a_{12}+a_{22})(a^\prime_{11}+a^\prime_{12}+a^\prime_{22}))\\ & = \chi_m(a_{11}a^\prime_{11}+a_{11}a^\prime_{12}+a_{12}a^\prime_{22}+a_{22}a^\prime_{22})\\ & = \varpi_m(a_{11})a^\prime_{11}+a_{11}\varpi_m(a^\prime_{11})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{11})d_j(a^\prime_{11})\\ &+\varpi_m(a_{11})a^\prime_{12}+a_{11}\varpi_m(a^\prime_{12})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{11})d_j(a^\prime_{12})\\ &+\varpi_m(a_{12})a^\prime_{22}+a_{12}\varpi_m(a^\prime_{22})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{12})d_j(a^\prime_{22})\\ &+\varpi_m(a_{22})a^\prime_{22}+a_{22}\varpi_m(a^\prime_{22})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{22})d_j(a^\prime_{22}). \end{aligned} \end{align} | (4.17) |
On the other hand, we have
\begin{aligned} &\chi_m(x)y+x\chi_m(y)+\sum\limits_{i+j = m, 0 < i < m}\chi_i(x)\chi_j(y)\\ & = \chi_m(a_{11}+a_{12}+a_{22})y+x\chi_m(a^\prime_{11}+a^\prime_{12}+a^\prime_{22})+\sum\limits_{i+j = m, 0 < i < m}\chi_i(x)\chi_j(y)\\ & = (\varpi_m(a_{11})+\varpi_m(a_{12})+\varpi_m(a_{22}))y+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{11})d_j(a^\prime_{11})\\ &+x(\varpi_m(a^\prime_{11})+\varpi_m(a^\prime_{12})+\varpi_m(a^\prime_{22}))+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{11})d_j(a^\prime_{12})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{11})d_j(a^\prime_{22})\\ &+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{12})d_j(a^\prime_{11})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{12})d_j(a^\prime_{12})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{12})d_j(a^\prime_{22})\\ &+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{22})d_j(a^\prime_{11})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{22})d_j(a^\prime_{12})+\sum\limits_{i+j = m, 0 < p < m}d_i(a_{22})d_j(a^\prime_{22}). \end{aligned} |
Taking into account the induction hypothesis \mathfrak{F}_s , Lemmas 4.9 and 4.10, we calculate that
\begin{align} \begin{aligned} &\chi_m(x)y+x\chi_m(y)+\sum\limits_{i+j = m, 0 < i < m}d_i(x)d_j(y)\\ & = \varpi_m(a_{11})a^\prime_{11}+\varpi_m(a_{11})a^\prime_{12}+\varpi_m(a_{12})a^\prime_{22}+\varpi_m(a_{22})a^\prime_{22}\\ &+a_{11}\varpi_m(a^\prime_{11})+a_{11}\varpi_m(a^\prime_{12})+a_{12}\varpi_m(a^\prime_{22})+a_{22}\varpi_m(a^\prime_{22})\\ &+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{11})d_j(a^\prime_{11})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{11})d_j(a^\prime_{12})\\ &+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{12})d_j(a^\prime_{22})+\sum\limits_{i+j = m, 0 < i < m}d_i(a_{22})d_j(a^\prime_{22}). \end{aligned} \end{align} | (4.18) |
Combining (4.18) and (4.19) , we get
\chi_m(xy) = \chi_m(x)y+x\chi_m(y)+\sum\limits_{i+j = m, 0 < i < m}\chi_i(x)\chi_j(y) |
for all x, y\in \mathcal{T} . This shows that each \chi_m satisfies the Leibniz formula of higher order on \mathcal{T} .
Finally, we need to prove that each h_m vanishes P_n(x_1, \cdots, x_n) with x_1\cdots x_n = 0 for all x_1, \cdots, x_n\in \mathcal{T} . Note that h_m maps into \mathcal{Z}(\mathcal{T}) , \{\chi_i\}^m_{i = 0} as an additive higher derivation of \mathcal{T} . It follows from inductive hypothesis \mathfrak{F}_s that
h_m(P_n(x_1, \cdots, x_n)) = \delta_n(P_n(x_1, \cdots, x_n))-\chi_n(P_n(x_1, \cdots, x_n)) = 0 |
with x_1\cdots x_n = 0 for all x_1, \cdots, x_n\in \mathcal{T} . We lastly complete the proof of the main theorem.
In particular, we have the following corollaries.
When n = 3 , we have the following corollary.
Corollary 4.1. [17,Theorem 3.3] Let \mathcal{T} = \left[\begin{array}{cc} A_{11} & A_{12}\\ O & A_{22} \end{array}\right] be a triangular algebra satisfying
\text{i}) \pi_{A_{11}}(\mathcal{Z}(\mathcal{T})) = \mathcal{Z}(\mathcal{A}_{11}) and \pi_{A_{22}}(\mathcal{Z}(\mathcal{T})) = \mathcal{Z}(\mathcal{A}_{22}) .
\text{ii}) For any a_{11}\in A_{11} , if [a_{11}, A_{11}]\in \mathcal{Z}(\mathcal{A})_{11} , then a_{11}\in \mathcal{Z}(\mathcal{A}) , or for any a_{22}\in A_{22} , if [a_{22}, A_{22}]\in \mathcal{Z}(\mathcal{A}_{22}) , then a_{22}\in \mathcal{Z}(\mathcal{A}_{22}) .
Suppose that a sequence \Delta = \{\delta_m\}_{m\in \mathcal{N}} of mappings \delta_m:\mathcal{T}\rightarrow \mathcal{T} is a nonlinear map satisfying
\delta_m([[x, y], z]) = \sum\limits_{i+j+k = m}[[\delta_i(x), \delta_j(y)], \delta_k(z)] |
for all x, y, z \in \mathcal{T} with xyz = 0 . For every m\in \mathcal{N} ,
\delta_m(x) = \chi_m(x)+h_m(x) |
for all x\in \mathcal{T} , where a sequence \Upsilon = \{\chi_m \}_{m\in \mathcal{N}} of additive mapping \chi_m:\mathcal{T}\rightarrow \mathcal{T} is a higher derivation and h_m:\mathcal{T}\rightarrow \mathcal{Z}(\mathcal{T}) is a nonlinear mapping, such that h_m([[x, y], z]) = 0 for any x, y, z\in \mathcal{T} with xyz = 0 .
When n = 3 and m = 1 , we have the following corollary.
Corollary 4.2. [16,Theorem 2.2] Let \mathcal{T} = \left[\begin{array}{cc} A_{11} & A_{12}\\ O & A_{22} \end{array}\right] be a triangular algebra satisfying
\text{i}) \pi_{A_{11}}(\mathcal{Z}(\mathcal{T})) = \mathcal{Z}(\mathcal{A}_{11}) and \pi_{A_{22}}(\mathcal{Z}(\mathcal{T})) = \mathcal{Z}(\mathcal{A}_{22}) .
\text{ii}) For any a_{11}\in A_{11} , if [a_{11}, A_{11}]\in \mathcal{Z}(\mathcal{A}_{11}) , then a_{11}\in \mathcal{Z}(\mathcal{A}) , or for any a_{22}\in A_{22} , if [a_{22}, A_{22}]\in \mathcal{Z}(\mathcal{A}_{22}) then a_{22}\in \mathcal{Z}(\mathcal{A}_{22}) .
Suppose \delta_1:\mathcal{T}\rightarrow \mathcal{T} is a nonlinear map satisfying
\delta_1([[x, y], z]) = \sum\limits_{i+j+k = 1}[[\delta_i(x), \delta_j(y)], \delta_k(z)] |
for all x, y, z \in \mathcal{T} with xyz = 0 , then there exists an additive derivation \varpi_1 of \mathcal{T} and a nonlinear map h_1:\mathcal{T}\rightarrow \mathcal{Z}(\mathcal{T}) , such that
\delta_1(x) = \chi_1(x)+h_1(x) |
for all x\in \mathcal{T} , where \tau_1([[x, y], z]) for any x, y, z\in \mathcal{T} with xyz = 0 .
In this section, we apply Theorem 4.2 to certain classes of triangular algebras that satisfy the hypotheses of Theorem 4.2. Some standard examples of triangular rings satisfying the hypotheses of Theorem 4.1 are: Upper triangular matrix algebras, block upper triangular matrix algebras and nest algebras (see [24,4. More applications and further topics] for details).
According to the Theorem 4.2, we get the following corollaries.
Corollary 5.1. Let \mathcal{R} be a 2 -torsion free commutative ring with identity and \mathcal{T}_k(\mathcal{R})(k\geq 2) be the algebra of all k\times n upper triangular matrices over \mathcal{R} . Let \{L_m\}_{m\in \mathcal{N}} be a family of nonlinear mapping L_m: \mathcal{T}_k(\mathcal{R})\longrightarrow \mathcal{T}_k(\mathcal{R}) satisfying Eq (1.3) , then every Lie- m higher derivation L_m: \mathcal{T}_k(\mathcal{R})\longrightarrow \mathcal{T}_k(\mathcal{R}) be of standard form.
Corollary 5.2. Let \mathcal{R} be a 2 -torsion free commutative ring with identity and \mathcal{T}_s^{\overline{k}}(\mathcal{R})(s\geq 3) be a block upper triangular matrix ring with over \mathcal{T}_s^{\overline{k}}(\mathcal{R})\neq M_s(R) . Let \{L_m\}_{m\in \mathcal{N}} be a family of nonlinear mapping L_m: \mathcal{T}_s^{\overline{k}}(\mathcal{R})\longrightarrow \mathcal{T}_s^{\overline{k}}(\mathcal{R}) satisfying Eq (1.3) , then every Lie- m higher derivation L_m: \mathcal{T}_s^{\overline{k}}(\mathcal{R})\longrightarrow \mathcal{T}_s^{\overline{k}}(\mathcal{R}) be of standard form.
Corollary 5.3. Let {\rm H} be a Hilbert space, \mathcal{N} be a nest of {\rm H} and {\rm Alg}(\mathcal{N}) be the nest algebra associated with \mathcal{N} . Let \{L_m\}_{m\in \mathcal{N}} be a family of nonlinear mapping L_m: {\rm Alg}(\mathcal{N})\longrightarrow {\rm Alg}(\mathcal{N}) satisfying Eq (1.3) , then every Lie- m higher derivation L_m: {\rm Alg}(\mathcal{N})\longrightarrow {\rm Alg}(\mathcal{N}) be of standard form.
The purpose of this article was to prove that every nonlinear Lie-n higher derivation by local actions on the triangular algebras is of a standard form. As an application, we gave a characterization of Lie- n higher derivations by local actions on upper triangular matrix algebras, block upper triangular matrix algebras and nest algebras, respectively.
The author declares she has not used Artificial Intelligence(AI) tools in the creation of this article.
This work was supported by the Youth fund of Anhui Natural Science Foundation (Grant No. 2008085QA01), Key projects of University Natural Science Research Project of Anhui Province (Grant No. KJ2019A0107) and National Natural Science Foundation of China (Grant No. 11801008).
The authors declare no conflicts of interest.
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