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
p1(δm(a11+a′11)−(δm(a11)+δm(a′11)))p2=0. | (4.4) |
Combining (4.5) and (4.6), this claim holds.
Lemma 4.5. With notations as above, we have δm(a11+x12+b22)−δm(a11)−δm(x12)−δm(b22)∈Z(T) for all a11∈A11,x12∈A12,a22∈A22.
Proof. For arbitrary a11∈A11,x12∈A12,a22∈A22, in view of (a11+x12+b22)x′12p1p2⋯p2=0, we have
δm(x12′b22−a11x′12)=δm(Pn(a11+x12+b22,x′12,p1,p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(a11+x12+b22),δi2(x′12),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies) |
and
δm(x′12b22−a11x′12)=δm(x′12b22)+δm(−a11x′12)=δm(Pn(a11,x′12,p1,p2,⋯,p2))+δm(Pn(x12,x′12,p1,p2,⋯,p2))+δm(Pn(b22,x′12,p1,p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(a11)+δi1(x12)+δi1(b22),δi2(x′12),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies). |
Let us set Wi=δi(a11+x12+b22)−(δi(a11)+δi(x12)+δi(b22)). Taking into accounts the above two equations and using inductive hypothesis Cs for all 1≤s≤n, we have
0=∑i1+⋯+in=mPn(Wi1,δi2(x′12),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies)=∑i1+⋯+in=m,i1≠mPn(Wi1,δi2(x′12),δi3(p1),δi4(p2),⋯,δin(p2)⏟n−3 copies)+Pn(Wm,x′12,p1,p2,⋯,p2⏟n−3 copies)=Pn(Wm,x′12,p1,p2,⋯,p2⏟n−3 copies), |
which is p1Wmx′12−x′12Wmp2=0, i.e.,
p1Wmp1⊕p2Wmp2∈Z(T). | (4.5) |
In the following part, we prove p1Wmp2=0. It is clear that (a11+x12+b22)(−p1)p2⋯p2⏟n−2 copies=0, then
δm(x12)=δm(Pn(a11+x12+b22,−p1,p2,⋯,p2⏟n−2 copies)=∑i1+⋯+in=mPn(δi1(a11+x12+b22),δi2(−p1),δi3(p2),⋯,δin(p2)⏟n−2 copies) |
and
δn(x12)=δm(Pn(a11,−p1,p2,⋯,p2⏟n−2 copies)+δm(Pn(x12,−p1,p2,⋯,p2⏟n−2 copies)+δm(Pn(b22,−p1,p2,⋯,p2⏟n−2 copies)=∑i1+⋯+in=mPn(δi1(a11)+δi1(x12)+δi1(b22),δi2(−p1),δi3(p2),⋯,δin(p2)⏟n−2 copies). |
According to the above two equations and inductive hypothesis Cs for all 1≤s≤m, we can get
0=∑i1+⋯+in=mPn(Wi1,δi2(−p1),δi3(p2),⋯,δin(p2)⏟n−2 copies)=∑i1+⋯+in=m,i1≠mPn(Wi1,δi2(−p1),δi3(p2),⋯,δin(p2)⏟n−2 copies)+Pn(Wm,−p1,p2,⋯,p2⏟n−2 copies)=Pn(Wm,−p1,p2,⋯,p2⏟n−2 copies), |
which is
p1Wmp2=0. | (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=a11+x12+b22 and y=a′11+x′12+b′22, we have
δm(x+y)=δm(a11+a′11+x12+x′12+b22+b′22)=δm(a11+a′11)+δm(x12+x′12)+δm(b22+b′22)+Z1=δm(a11)+δm(a′11)+δm(x12)+δm(x′12)+δm(b22)+δm(b′22)+Z1+Z2+Z3=δm(x)+δm(y)+Z1+Z2+Z3+Z4+Z5, |
which implies that δm(x+y)−δm(x)−δm(y)∈Z(T).
Based on the additive of δm on T, we give the main result in this section reading as follows.
Theorem 4.2. 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 sequence Δ={δm}m∈N of mappings δm:T→T is a nonlinear map satisfying
δm(Pn(x1,x2,⋯,xn))=∑i1+⋯+in=mPn(δi1(x1),δi2(x2),⋯,δin(xn)) |
for all x1,x2,⋯,xn∈T with x1x2⋯xn=0 and n≥3. For every m∈N,
δm(x)=χm(x)+fm(x) |
for all x∈T, where a sequence Υ={χm}m∈N of additive mapping χm:T→T is a higher derivation, and fm:T→Z(T) is a nonlinear mapping such that fm(Pn(x1,x2,⋯,xn))=0 for any x1,x2,⋯,xn∈T with x1x2⋯xn=0.
In the process of proof, we will use mathematical induction for index m. For m=1, δ1=Ln is a Lie-n derivation on T by local action at zero. By Theorem 3.2, it follows from Theorem 3.2 that there exists an additive derivation d1 and a nonlinear center mapping f1, satisfying f1(Pn(x1,x2,⋯,xn))=0 for any x1,x2,⋯,xn∈T with x1x2⋯xn=0 and n≥3, such that δ1(x)=d1(x)+f1(x) for all x∈T. Furthermore, δ1 and d1 satisfy the following properties
F1={δ1(0)=0,δ1(A11)⊆A11+A12+Z(T),δ1(A22)⊆A22+A12+Z(T);δ1(A12)⊆A12,δ1(pi)⊆A12+Z(T);d1(Aii)⊆Aii+Aij,d1(A12)⊆A12;f1(Pn(x1,x2,⋯,xn))=0 |
for i≤j∈{1,2} and for any x1,⋯,xn∈T with x1⋯xn=0.
We assume that the result holds for s for all 1<s<m, m∈N, then there exists an additive derivation ds and a nonlinear center mapping fs, satisfying fs(Pn(x1,x2,⋯,xn))=0 for any x1,x2,⋯,xn∈T with x1x2⋯xn=0, such that δs(x)=ds(x)+fs(x) for all x∈T. Moreover, δs and ds satisfy the following properties
Fs={δs(0)=0,δ1(A11)⊆A11+A12+Z(T),δ1(A22)⊆A22+A12+Z(T);δs(A12)⊆A12,δs(pi)⊆A12+Z(T);ds(Aii)⊆Aii+Aij,ds(A12)⊆A12;fs(Pn(x1,x2,⋯,xn))=0 |
for i≤j∈{1,2} and for any x1,x2,⋯,xn∈T with x1x2⋯xn=0.
The induction process can be realized through a series of lemmas.
Lemma 4.6. With notations as above, we have
1) δm(A12)⊆A12;
2) p1δm(p1)p1⊕p2δm(p1)p2∈Z(T) and p1δm(p2)p1⊕p2δm(p2)p2∈Z(T);
3) δm(p1)∈M12+Z(T).
Proof. Because of x12p1p1p2⋯p2⏟n−3 copies=0 for x12∈A12, with the help of condition Fs for all 1<s<m, we have
δm(x12)=δm(Pn(x12,p1,p1,p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(x12),δi2(p1),δi3(p1),δi4(p2),⋯,δin(p2))=∑i1+⋯+in=m,0<i1,⋯,in<mPn(δi1(x12),δi2(p1),δi3(p1),δi4(p2),⋯,δin(p2))+Pn(δm(x12),p1,p1,p2,⋯,p2)+Pn(x12,δm(p1),p1,p2,⋯,p2)+Pn(x12,p1,δm(p1),p2,⋯,p2)+n∑s=4Pn(x12,p1,p1,p2,⋯,p2,δm(p2)⏟s−th component,⋯,p2)=Pn(δm(x12),p1,p1,p2,⋯,p2)+Pn(x12,δm(p1),p1,p2,⋯,p2)+Pn(x12,p1,δm(p1),p2,⋯,p2)=p1δm(x12)p2+p1δm(p1)x12+δm(p1)x12−2x12δm(p1), |
then we can obtain that δm(x12)∈A12. Multiplying by p1 on the left side and p2 on the right side of the above equation, we can obtain that p1δm(p1)x12=x12δm(p1)p2 for all x12∈A12. It follows from definition of center that
p1δm(p1)p1⊕p2δm(p1)p2∈Z(T). |
Because of p2x12p1p2⋯p2=0, we adopt the same discussion as relations
δm(x12)=δm(Pn(p2,x12,p1,p2⋯,p2))=∑i1+⋯+in=mPn(δi1(p2),δi2(x12),δi3(p1),δi4(p2),⋯,δin(p2))=∑i1+⋯+in=m,0<i1,⋯,in<mPn(δi1(p2),δi2(x12),δi3(p1),δi4(p2),⋯,δin(p2))+Pn(δm(p2),x12,p1,p2,⋯,p2)+Pn(p2,δm(x12),p1,p2,⋯,p2)+Pn(p2,x12,δm(p1),p2,⋯,p2)+n∑s=4Pn(p2,x12,p1,p2,⋯,p2,δm(p2)⏟s−th component,⋯,p2)=Pn(δm(p2),x12,p1,p2,⋯,p2)+Pn(p2,δm(x12),p1,p2,⋯,p2)+Pn(p2,x12,δm(p1),p2,⋯,p2)=−p1δm(p2)x12+x12δm(p2)p2+p1δm(x12)p2−x12δm(p1)p2+δm(p1)x12=−p1δm(p2)x12+x12δm(p2)p2+p1δm(x12)p2 |
Multiplying by p1 on the left side and p2 on the right side of the above equation, we can obtain that p1δm(p2)x12=x12δm(p2)p2 for all x12∈A12. It follows from definition of center and we can prove that p1δm(p2)p1⊕p2δm(p2)p2∈Z(T) holds.
Lemma 4.7. With notations as above, we have
1) δm(a11)∈A11+A12+Z(T), where p2δm(a11)p2∈Z(A11);
2) δm(a22)∈A22+A12+Z(T), where p1δm(a22)p1∈Z(A22)
for all aii∈Aii with i∈{1,2}.
Proof. In fact, it is clear that a22a11a12p2⋯p2⏟n−3 copies=0 for all aij∈Aij and for all i,j∈{1,2}, then according to inductive hypothesis Fs, we have
0=δm(Pn(a22,a11,a12,p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(a22),δi2(a11),δi3(a12),δi4(p2),⋯,δin(p2))=∑i1+⋯+in=m,i1,⋯,in<mPn(δi1(a22),δi2(a11),δi3(a12),δi4(p2),⋯,δin(p2))+Pn(δm(a22),a11,a12,p2,⋯,p2)+Pn(a22,δm(a11),a12,p2,⋯,p2)=Pn(δm(a22),a11,a12,p2,⋯,p2)+Pn(a22,δm(a11),a12,p2,⋯,p2)=Pn(p1δm(a22)p1,a11,a12,p2,⋯,p2)+Pn(a22,p2δm(a11)p2,a12,p2,⋯,p2)=Pn−1([p1δm(a22)p1,a11]+[a22,p2δm(a11)p2],a12,p2,⋯,p2) |
for all aij∈Aij and for all i≤j∈{1,2}. In light of Lemma 3.1, we obtain
[p1δm(a22)p1,a11]⊕[a22,p2δm(a11)p2]∈Z(T) | (4.7) |
for all aii∈Aii and or all i∈{1,2}. With the help of characterization of algebraic center, we have
[p1δm(a22)p1,a11]∈Z(A11) and [a22,p2δm(a11)p2]∈Z(A22), |
then
p1δm(a22)p1∈Z(A11) and p2δm(a11)p2∈Z(A22) | (4.8) |
for all aii∈Aii and for all i∈{1,2}. Further based on theorem hypothesis (ii) and above Eqs (4.9) and (4.10), we arrive at
δm(a11)=p1δm(a11)p1−τ−1(p2δm(a11)p2)+p1δm(a11)p2+τ−1(p2δm(a11)p2)+p2δm(a11)p2∈A11+A12+Z(T) |
and
δm(a22)=p2δm(a22)p2−τ(p1δm(a22)p1)+p1δm(a22)p2+p1δm(a22)p1+τ(p1δm(a22)p1)∈A22+A12+Z(T) |
for all aij∈Aij with i≤j∈{1,2}. We can conclude that this claim can be established.
Now, we define mapping fm1(a11)=τ−1(p2δm(a11)p2)+p2δm(a11)p2 and fm2(a22)=p1δm(a22)p1+τ(p1δm(a22)p1) for all a11∈A11 and a22∈A22. It follows from Lemma 4.7 that fm1:A11→Z(A11) such that fn1(Pn(a111,⋯,an11))=0 for all a111,⋯,an11∈A11 with a111a211⋯an11=0 and fm2:A22→Z(A22), such that fm2(Pn(a122,⋯,an22))=0 for all a122,⋯,an22∈A22 with a122a222⋯an22=0. Now, set
fm(x)=fm1(a11)+fm2(a22)=τ−1(p2δm(a11)p2)+p2δm(a11)p2+p1δm(a22)p1+τ(p1δm(a22)p1) | (4.9) |
for all x=a11+a12+a22∈T. It is clear that fm(x)∈Z(T) and fm(Pn(x1,x2,⋯,xn))=0 with x1x2⋯xn=0 for all x1,x2,⋯,xn∈T. Define a new mapping
ϖm(x)=δm(x)−fm(x) | (4.10) |
for all x∈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) ϖm(0)=0, ϖm(a12)=δm(a12)∈A12, ϖm(pi)∈A12;
2) ϖm(a11)∈A11+A12 and ϖm(a22)∈A22+A12,
for all aij∈Aij with i≤j∈{1,2}.
Lemma 4.9. With notations as above, we have
1) ϖm(a11a12)=a11ϖm(a12)+ϖm(a11)a12+∑i+j=m,0<i,j<mdi(a11)dj(a12);
2) ϖm(a12a22)=a12ϖm(a22)+ϖm(a12)a22+∑i+j=n,0<i,j<mdi(a12)dj(a22)
for all aij∈Aij with i≤j∈{1,2}.
Proof. Now, we only prove the conclusion 1), and conclusion 2) can be proved by similar methods. It follows from a12a11p1p2⋯p2⏟n−3 copies=0 and the induction hypothesis Fs for all 1≤s≤m−1 that
ϖm(a11a12)=δm(a11a12)=δm(Pn(a12,a11,p1,p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(a12),δi2(a11),δi3(p1),δi4(p2),⋯,δin(p2))=∑i1+⋯+in=m,i1,⋯,in<mPn(δi1(a12),δi2(a11),δi3(p1),δi4(p2),⋯,δin(p2))+Pn(δm(a12),a11,p1,p2,⋯,p2)+Pn(a12,δm(a11),p1,p2,⋯,p2)+Pn(a12,a11,δm(p1),p2,⋯,p2)=∑i1+⋯+in=m,i1,⋯,in<mPn(di1(a12),di2(a11),di3(p1),di4(p2),⋯,din(p2))+a11ϖn(a12)+ϖn(a11)a12=∑i1+i2=m,0<i1,i2<mPn(di1(a12),di2(a11),p1,p2,⋯,p2)+a11ϖn(a12)+ϖn(a11)a12=a11ϖn(a12)+ϖn(a11)a12+∑i1+i2=m,0<i1,i2<mdi2(a11)di1(a12) |
for all ast∈Ast with s≤t∈{1,2}.
Adopt the same discussion as relations ϖm(a12a22)=δm(a12a22)=δm(Pn(a22,a12,p1,p2,⋯,p2)) with a22a12p1p2⋯p2=0, and we can prove
ϖn(a12a22)=a12ϖn(a22)+ϖn(a12)a22+∑i+j=n,0<i,j<ndi(a12)dj(a22) |
for all ast∈Ast with s≤t∈{1,2}.
Lemma 4.10. With notations as above, we have
1) ϖm(a11a′11)=ϖm(a11)a′11+a11ϖm(a′11)p2+∑i+j=m,0<i,j<mdi(a11)dj(a′11);
2) ϖm(b22b′22)=ϖm(b22)b′22+b22ϖm(b′22)p2+∑i+j=n,0<i,j<mdi(b22)dj(b′22)
for all aii,a′ii∈Aii with i∈{1,2}.
Proof. For conclusion 1), arbitrary a11,a′11∈A11 and a12∈A12 and by conclusion 1) in Lemma 4.9, we have
ϖm(a11a′11a12)=a11a′11ϖm(a12)+ϖm(a11a′11)a12+∑i+j=m,0<i,j<mdi(a11a′11)dj(a12)=a11a′11ϖm(a12)+ϖm(a11a′11)a12+∑i+j=m,0<i,j<m(∑i1+i2=i,0<i<mdi1(a11)di2(a′11))dj(a12)=a11a′11ϖm(a12)+ϖm(a11a′11)a12+∑i1+i2+j=m,0<i1,i2,j<mdi1(a11)di2(a′11)dj(a12) | (4.11) |
and
ϖm(a11a′11a12)=a11ϖm(a′11a12)+ϖm(a11)a′11a12+∑i+j=m,0<i,j<mdi(a11)dj(a′11a12)=a11a′11ϖm(a12)+a11ϖm(a′11)a12+ϖm(a11)a′11a12+∑i+j=n,0<i,j<ma11di(a′11)dj(a12)+∑i+j=m,0<i,j<mdi(a11)dj(a′11a12)=a11a′11ϖm(a12)+a11ϖm(a′11)a12+ϖm(a11)a′11a12+∑i+j=m,0<i,j<ma11di(a′11)dj(a12)+∑i+j=m,0<i,j<mdi(a11)(∑j1+j2=j,0<j<mdj1(a′11)dj2(a12))=a11a′11ϖm(a12)+a11ϖm(a′11)a12+ϖm(a11)a′11a12+∑i+j=m,0<i,j<ma11di(a′11)dj(a12)+∑i+j1+j2=m,0<i,j1,j2<mdi(a11)dj1(a′11)dj2(a12)=a11a′11ϖm(a12)+a11ϖm(a′11)a12+ϖm(a11)a′11a12+∑i+j=m,0<i,j<mdi(a11)dj(a′11)a12+∑i+j1+j2=m,0<i,j1,j2<mdi(a11)dj1(a′11)dj2(a12) | (4.12) |
for all att,a′tt∈Att with t∈{1,2}.
Combining (4.12) with (4.13) leads to
ϖm(a11a′11)a12=(ϖm(a11)a′11+a11ϖm(a′11)+∑i+j=m,0<i,j<mdi(a11)dj(a′11))a12 |
for all att,a′tt∈Att with t∈{1,2}.
Since ϖm(A11)⊆A11+A12 and A12 are faithful as a left A11-module, the above relation implies that
ϖm(a11a′11)p1={ϖm(a11)a′11+a11ϖm(a′11)+∑i+j=m,0<i,j<mdi(a11)dj(a′11)}p1 | (4.13) |
for all a11,a′11∈A11.
On the other hand, by a11p2⋯p2⏟n−1 copies=0 for all a11∈A11, we arrive at
0=δm(Pn(a11,p2,⋯,p2⏟n−1 copies))=Pn(δm(a11),p2,⋯,p2⏟n−1 copies)+Pn(a11,δm(p2),p2,⋯,p2⏟n−2 copies)+∑i1+⋯+in=m,i1,⋯,in<mPn(δi1(a11),δi2(p2),⋯,δin(p2))=Pn(ϖm(a11),p2,⋯,p2⏟n−1 copies)+Pn(a11,ϖm(p2),p2,⋯,p2⏟n−2 copies)+∑i1+⋯+in=m,i1,⋯,in<mPn(di1(a11),di2(p2),⋯,din(p2)) |
for all a11,a′11∈A11.
Since ϖn(A11)⊆A11+A12,ϖn(p2)∈A12 and di(p2)∈A12, the above equation implies that
0=ϖm(a11)p2+a11ϖm(p2)+∑i+j=m,0≤i,j<mdi(a11)dj(p2) |
for all a11,a′11∈A11.
On substituting a11 by a11a′11 in above equation, we get
0=ϖm(a11a′11)p2+a11a′11ϖm(p2)+∑i+j=m,0≤i,j<mdi(a11a′11)dj(p2)=ϖm(a11a′11)p2+a11a′11ϖm(p2)+∑i+j=m,0≤i,j<m(∑i1+i2=i,0≤i1,i2<mdi1(a11)di2(a′11))dj(p2)=ϖm(a11a′11)p2+a11a′11ϖm(p2)+∑i1+i2+j=m,0≤i1,i2,j<mdi1(a11)di2(a′11)dj(p2) |
for all a11,a′11∈A11. Therefore, we have
p1(ϖm(a11a′11)p2+a11a′11ϖm(p2)+∑i1+i2+j=m,0≤i1,i2,j<mdi1(a11)di2(a′11)dj(p2))p2=0. | (4.14) |
Again, note that a′11p2⋯p2=0 for all a′11∈A11, and we have
0=δm(Pn(a′11,p2,⋯,p2))=∑i1+⋯+in=mPn(δi1(a′11),δi2(p2),⋯,δin(p2))=Pn(ϖm(a′11),p2,⋯,p2)]+Pn(a′11,ϖm(p2),p2,⋯,p2]+∑i1+⋯+in=m,i1,⋯,in<mPn(di1(a′11),di2(p2),⋯,din(p2)). |
This gives us
0=ϖm(a′11)p2+a′11ϖm(p2)+∑i+j=m,0≤i,j<mdi(a′11)dj(p2). | (4.15) |
Now, left multiplying a11 in (4.16) and combining it with (4.15) gives us
ϖm(a11a′11)p2+∑i+j+k=m,0≤i,0<jdi(a11)dj(a′11)dk(p2)=a11ϖm(a′11)p2. |
This implies that
ϖm(a11a′11)p2+m∑i=1di(a11)∑j+k=m−i,0≤idj(a′11)dk(p2)=a11ϖm(a′11)p2. |
Now, using the condition Fs, we find that
ϖm(a11a′11)p2−m−1∑i=1di(a11)dm−i(a′11)p2=a11ϖm(a′11)p2, |
which gives
ϖm(a11a′11)p2=a11ϖm(a′11)p2+m−1∑i=1di(a11)dm−i(a′11)p2. |
Hence,
ϖm(a11a′11)p2={ϖm(a11)a′11+a11ϖm(a′11)p2+∑i+j=m,0<i,j<mdi(a11)dm−i(a′11)}p2. | (4.16) |
Now, adding (4.14) and (4.17), we have
ϖm(a11a′11)=ϖm(a11)a′11+a11ϖm(a′11)p2+∑i+j=m,0<i,j<mdi(a11)dj(a′11). |
Adopting the same discussion, we have
ϖm(b22b′22)=ϖm(b22)b′22+b22ϖm(b′22)p2+∑i+j=m,0<i,j<mdi(b22)dj(b′22) |
for all b22,b′22∈A22.
Remark 4.1. Now, we establish a mapping gm:T→Z(T) by
gm(x)=ϖm(x)−ϖm(p1xp1)−ϖm(p1xp2)−ϖm(p2xp2) |
and gm(Pn(x1,⋯,xn))=0 with x1⋯xn=0 for all x1,⋯,xn∈T, then define a mapping χm(x)=ϖm(x)−gm(x) for all x∈T. It is easy to verify that
χm(a11+a12+a22)=χm(a11)+χm(a12)+χm(a22). |
From the definition of χm and gm, we find that
φm(x)=ϖm(x)+fm(x)=χm(x)+gm(x)+fm(x)=χm(x)+hm(x), |
where hm(x)=gm(x)+fm(x) for all x∈T.
Lemma 4.11. With notations as above, we obtain that {χi}i=mi=0 is an additive higher derivation on triangular algebras T.
Proof. Suppose that x,y∈T, such that x=a11+a12+a22 and y=a′11+a′12+a′22, where aij,a′ij∈Aij with i⩽j∈{1,2}, then
χm(x+y)=χm((a11+a12+a22)+(a′11+a′12+a′22))=χm((a11+a′11)+(a12+a′12)+(a22+a′22))=χm(a11+a′11)+χm(a12+a′12)+χm(a22+a′22)=χm(a11)+χm(a′11)+ϖm(a12)+χm(a′12)+χm(a22)+χm(a′22)=χm(a11+a12+a22)+χm(a′11+a′12+a′22))=χm(x)+χm(y). |
By Lemmas 4.8 and 4.10, we have
χm(xy)=χm((a11+a12+a22)(a′11+a′12+a′22))=χm(a11a′11+a11a′12+a12a′22+a22a′22)=ϖm(a11)a′11+a11ϖm(a′11)+∑i+j=m,0<i<mdi(a11)dj(a′11)+ϖm(a11)a′12+a11ϖm(a′12)+∑i+j=m,0<i<mdi(a11)dj(a′12)+ϖm(a12)a′22+a12ϖm(a′22)+∑i+j=m,0<i<mdi(a12)dj(a′22)+ϖm(a22)a′22+a22ϖm(a′22)+∑i+j=m,0<i<mdi(a22)dj(a′22). | (4.17) |
On the other hand, we have
χm(x)y+xχm(y)+∑i+j=m,0<i<mχi(x)χj(y)=χm(a11+a12+a22)y+xχm(a′11+a′12+a′22)+∑i+j=m,0<i<mχi(x)χj(y)=(ϖm(a11)+ϖm(a12)+ϖm(a22))y+∑i+j=m,0<i<mdi(a11)dj(a′11)+x(ϖm(a′11)+ϖm(a′12)+ϖm(a′22))+∑i+j=m,0<i<mdi(a11)dj(a′12)+∑i+j=m,0<i<mdi(a11)dj(a′22)+∑i+j=m,0<i<mdi(a12)dj(a′11)+∑i+j=m,0<i<mdi(a12)dj(a′12)+∑i+j=m,0<i<mdi(a12)dj(a′22)+∑i+j=m,0<i<mdi(a22)dj(a′11)+∑i+j=m,0<i<mdi(a22)dj(a′12)+∑i+j=m,0<p<mdi(a22)dj(a′22). |
Taking into account the induction hypothesis Fs, Lemmas 4.9 and 4.10, we calculate that
χm(x)y+xχm(y)+∑i+j=m,0<i<mdi(x)dj(y)=ϖm(a11)a′11+ϖm(a11)a′12+ϖm(a12)a′22+ϖm(a22)a′22+a11ϖm(a′11)+a11ϖm(a′12)+a12ϖm(a′22)+a22ϖm(a′22)+∑i+j=m,0<i<mdi(a11)dj(a′11)+∑i+j=m,0<i<mdi(a11)dj(a′12)+∑i+j=m,0<i<mdi(a12)dj(a′22)+∑i+j=m,0<i<mdi(a22)dj(a′22). | (4.18) |
Combining (4.18) and (4.19), we get
χm(xy)=χm(x)y+xχm(y)+∑i+j=m,0<i<mχi(x)χj(y) |
for all x,y∈T. This shows that each χm satisfies the Leibniz formula of higher order on T.
Finally, we need to prove that each hm vanishes Pn(x1,⋯,xn) with x1⋯xn=0 for all x1,⋯,xn∈T. Note that hm maps into Z(T), {χi}mi=0 as an additive higher derivation of T. It follows from inductive hypothesis Fs that
hm(Pn(x1,⋯,xn))=δn(Pn(x1,⋯,xn))−χn(Pn(x1,⋯,xn))=0 |
with x1⋯xn=0 for all x1,⋯,xn∈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 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(A)11, then a11∈Z(A), or for any a22∈A22, if [a22,A22]∈Z(A22), then a22∈Z(A22).
Suppose that a sequence Δ={δm}m∈N of mappings δm:T→T is a nonlinear map satisfying
δm([[x,y],z])=∑i+j+k=m[[δi(x),δj(y)],δk(z)] |
for all x,y,z∈T with xyz=0. For every m∈N,
δm(x)=χm(x)+hm(x) |
for all x∈T, where a sequence Υ={χm}m∈N of additive mapping χm:T→T is a higher derivation and hm:T→Z(T) is a nonlinear mapping, such that hm([[x,y],z])=0 for any x,y,z∈T with xyz=0.
When n=3 and m=1, we have the following corollary.
Corollary 4.2. [16,Theorem 2.2] 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(A), or for any a22∈A22, if [a22,A22]∈Z(A22) then a22∈Z(A22).
Suppose δ1:T→T is a nonlinear map satisfying
δ1([[x,y],z])=∑i+j+k=1[[δi(x),δj(y)],δk(z)] |
for all x,y,z∈T with xyz=0, then there exists an additive derivation ϖ1 of T and a nonlinear map h1:T→Z(T), such that
δ1(x)=χ1(x)+h1(x) |
for all x∈T, where τ1([[x,y],z]) for any x,y,z∈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 R be a 2-torsion free commutative ring with identity and Tk(R)(k≥2) be the algebra of all k×n upper triangular matrices over R. Let {Lm}m∈N be a family of nonlinear mapping Lm:Tk(R)⟶Tk(R) satisfying Eq (1.3), then every Lie-m higher derivation Lm:Tk(R)⟶Tk(R) be of standard form.
Corollary 5.2. Let R be a 2-torsion free commutative ring with identity and T¯ks(R)(s≥3) be a block upper triangular matrix ring with over T¯ks(R)≠Ms(R). Let {Lm}m∈N be a family of nonlinear mapping Lm:T¯ks(R)⟶T¯ks(R) satisfying Eq (1.3), then every Lie-m higher derivation Lm:T¯ks(R)⟶T¯ks(R) be of standard form.
Corollary 5.3. Let H be a Hilbert space, N be a nest of H and Alg(N) be the nest algebra associated with N. Let {Lm}m∈N be a family of nonlinear mapping Lm:Alg(N)⟶Alg(N) satisfying Eq (1.3), then every Lie-m higher derivation Lm:Alg(N)⟶Alg(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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