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Research article

An application of generalized Morrey spaces to unique continuation property of the quasilinear elliptic equations

  • In this paper, we study nonnegative weak solutions of the quasilinear elliptic equation div(A(x,u,u))=B(x,u,u), in a bounded open set Ω, whose coefficients belong to a generalized Morrey space. We show that log(u+δ), for u a nonnegative solution and δ an arbitrary positive real number, belongs to BMO(B), where B is an open ball contained in Ω. As a consequence, this equation has the strong unique continuation property. For the main proof, we use approximation by smooth functions to the weak solutions to handle the weak gradient of the composite function which involves the weak solutions and then apply Fefferman's inequality in generalized Morrey spaces, recently proved by Tumalun et al. [1].

    Citation: Nicky K. Tumalun, Philotheus E. A. Tuerah, Marvel G. Maukar, Anetha L. F. Tilaar, Patricia V. J. Runtu. An application of generalized Morrey spaces to unique continuation property of the quasilinear elliptic equations[J]. AIMS Mathematics, 2023, 8(11): 26007-26020. doi: 10.3934/math.20231325

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  • In this paper, we study nonnegative weak solutions of the quasilinear elliptic equation div(A(x,u,u))=B(x,u,u), in a bounded open set Ω, whose coefficients belong to a generalized Morrey space. We show that log(u+δ), for u a nonnegative solution and δ an arbitrary positive real number, belongs to BMO(B), where B is an open ball contained in Ω. As a consequence, this equation has the strong unique continuation property. For the main proof, we use approximation by smooth functions to the weak solutions to handle the weak gradient of the composite function which involves the weak solutions and then apply Fefferman's inequality in generalized Morrey spaces, recently proved by Tumalun et al. [1].



    Labeling graphs have attracted the attention of numerous researchers in different disciplines. The importance of this research line is in fact due to the following:

    (1) Finding different coding techniques for securing the communication networks and database managements.

    (2) Providing a high-level secrecy to military services which is the most important factor for coding.

    (3) Providing confidentiality, and integrity of messages transferred between group members which is a critical networking issue. For more application, see [1,2].

    Coding through special kinds of graphs with different kinds of labeling is structured by many papers. Coding with Fibonacci web graph using super mean labeling was introduced by Uma Maheswari et al. [3]. Prasad et al. developed a technique of coding secret messages using sun flower graphs SFn. Furthermore, every labeling graph can be converted to a code by using GMJ coding methods (see, [4] and the references therein)

    A graph G is a pair (V,E), where V(G) and E(G) denote the vertex set and edge set of a graph G. The position of the vertices and the length of the edges do not concern us, what is important is the size of a graph (number of vertices) and the pairs of vertices which are connected by an edge. If e={u,v} is an edge of a graph G, then u and v are adjacent while u and e are incident. Let q=|E(G)| be the cardinality of E(G) and p=|V(G)| be that of V(G). For every vertex uV(G), the open neighborhood set N(u) is the set of all vertices adjacent to u in G. Graph operations[5] allow us to generate many new graphs from old ones. A fan graph Fn is defined as the join Pn+K1 where Pn is the path graph on n vertices and K1 is a complete graph on one vertex. The crown graph Crn(Sunlet graph) is the graph on 2n vertices obtained by attaching n pendant edges to a cycle graph Cn, i.e., the coronas CnK1.

    Definition 1.1. (i) The splitting graph S(G) of a connected graph G is the graph obtained by adding new vertex ui corresponding to each vertex vi of V(G) such that N(vi)=N(ui).

    (ii) The shadow graph D2(G) of a connected graph G is constructed by taking two copies of G, say G1 and G2. Join each vertex vi in G1 to the neighbors of the corresponding vertex ui in G2. The shadow graph D2(G) can be obtained from the splitting graph S(G) by adding edge between any two new vertices ui and uj if the corresponding original vertices vi and vj are adjacent. V[D2(G)]=V[S(G)], E[D2(G)]=E[S(G)]{uiui+1,i=1,2,,n}.

    (iii) The middle graph M(G) of a connected graph G is the graph whose vertex set is V(G)E(G) and in which two vertices in M(G) are adjacent whenever either they are adjacent edges of G or one is a vertex of G and the other is an edge incident with it.

    (iv) The total graph T(G) of a connected graph G is a graph such that the vertex set of T(G) corresponds to the vertices and edges of G and two vertices are adjacent in T(G) if their corresponding elements are either adjacent or incident in G. The total graph T(G) can be obtained from the middle graph M(G) by adding edge between any two original vertices vi and vj if the corresponding new vertices ui and uj are adjacent. V[T(G)]=V[M(G)], E[T(G)]=E[M(G)]E(G).

    There are many different kinds of graph labeling[6,7,8,9,10,11,12,13], all that kinds of labeling problem will have following three common characteristics. A set of numbers from which vertex or edge labels are chosen, A rule that assigns a value to each edge or vertex, A condition that these values must satisfy. For a comprehensive survey on graph labeling refers to a dynamic survey of graph labeling [14].

    Zeen El Deen [15] introduced the edge δ graceful labeling of graphs by using the numbers {δ,2δ,3δ, ,qδ} to label the edges of a graph, for any positive integer δ. He showed edge δ graceful labeling for some graphs related to cycles.

    Definition 1.2. An edge δ graceful labeling of a graph G=(V(G),E(G)) with p=|V(G)| vertices and q=|E(G)| edges is a bijective mapping f of the edge set E(G) into the set {δ,2δ,3δ,,qδ} such that the induced mapping f:V(G){0,δ,2δ,3δ,,kδδ}, given by: f(u)=(uvE(G)f(uv))mod(δk), where k=max(p,q), is an injective function. The graph that admits an edge δ graceful labeling is called an edge δ graceful graph, if δ=2 we have the edge even labeling also if δ=3 we have the edge triple labeling and so on.

    Example 1.1. In Figure 1 we present an edge δ graceful labeling of a tree graph on p=11 vertices and q=10 edges f:E(G){δ,2δ,3δ,,10δ} and f:V(G){0,δ,2δ,3δ,,10δ}, given by: f(u)=(uvE(G)f(uv))mod(11δ).

    Figure 1.  A tree with edge δ graceful labeling.

    Example 1.2. Duplication of an edge e=(xy) by a new vertex u in a graph G produces a new graph H such that N(u)={x,y}. Let {v1,v2,,vn} be the vertex set in the path Pn and G be the graph obtained by duplication of each edge vivi+1 of path Pn by vertex ui,(1i<n). Then V(G)=V(Pn){u1,u2,,un1} and the edge set are {vivi+1,viui,uivi+1,i=1,2,,n1}, so the graph G has p=2n1 vertices and q=3n3 edges, k=max(p,q)=3n3. An edge 5 graceful labeling of a graph obtained duplication of each edge of P11 by a vertex is shown in Figure 2.

    Figure 2.  Graph obtained duplication of each edge of P11 by a vertex and its edge 5 graceful labeling.

    Theorem 2.1. For any positive integer δ, the splitting graph S(Cn) of the cycle Cn,n>3 is an edge δ graceful graph.

    Proof. Let {v1,v2,,vn} be the vertices of Cn where these vertices are in their natural order module n. To form the splitting graph S(Cn) we add new vertices {u1,u2,,un} corresponding to vertices of Cn. The edges set of S(Cn) are {vivi+1,viui+1,uivi+1,i=1,2,,n}, the graph S(Cn) has p=2n vertices and q=3n edges, k=max(p,q)=3n.

    Case (1): When n2mod4,n>3. We define the labeling function f:E(S(Cn)){δ,2δ,,(3n)δ} as follows:

    f(viui+1)=δ(i),for1in,
    f(vivi+1)={δ(n+1),if i=1;δ(2n1+i),if 2in
    f(uivi+1)={δ(2n),if i=1;δ(n+i),if 2in1δ(3n),if i=n.

    In view of the above labeling pattern then the induced vertex labels are:

    f(v1)=(n+1)δ,f(v2)=(2n+4)δ,f(u1)=0,f(un)=(n1)δ, and

    f(vi)=(2n+4i4)δmod(3nδ),for3in,

    f(ui)=(n+2i1)δmod(3nδ),for2in1.

    Hence the vertex labels are all distinct and a multiple of δ.

    Case (2): When n0mod4,n=4, the graph S(C4) is an edge δ graceful graph for any positive integer δ define the labeling function f:E(S(C4)){δ,2δ,,(12)δ} as shown in Figure 3.

    Figure 3.  The splitting graphs S(C4) with an edge δ graceful labeling.

    When n0mod4,n>4, we define the labeling function f as follows:

    f(uivi+1)=δ(n+i),for1in,
    f(viui+1)={δ(i+1),if 2in1;δ,if i=n
    f(vivi+1)={δ(2n+i),if 1in3;δ(4n2i),if n2in.

    In view of the above labeling pattern then the induced vertex labels are:

    f(v1)=(n+1)δ,f(vn2)=(3n7)δ,f(vn1)=(3n3)δ,f(vn)=(2n3)δ,

    f(vi)=(2n+4i1)δmod(3nδ),for2in3,

    f(u1)=(n+2)δ,f(ui)=(n+2i)δmod(3nδ),for2in.

    Hence the vertex labels are all distinct and a multiple of δ.

    Case (3): When n is odd, we define the labeling function f as follows:

    f(uivi+1)=δ(3i2),for1in,f(vivi+1)=δ(3i1),for1in,f(viui+1)=δ(3i),for1in.

    In view of the above labeling pattern then the induced vertex labels are:

    f(vi)=(12i10)δmod(3nδ),for1in, and f(ui)=(6i5)δmod(3nδ),for1in

    Hence the vertex labels are all distinct and a multiple of δ. Therefore S(Cn) admits an edge δ graceful labeling.

    Illustration: The splitting graphs S(C8) with an edge 4 graceful labeling, S(C9) with an edge 5 graceful labeling and splitting graph S(C10) with an edge 3 graceful labeling are shown in Figure 4.

    Figure 4.  The splitting graphs S(C8) with an edge 4 graceful labeling, S(C9) with an edge 5 graceful labeling and D2(C10) with an edge 3 graceful labeling.

    Theorem 2.2. For any positive integer δ, the splitting graph S(Fn) of the fan graph Fn is an edge δ graceful graph.

    Proof. Let {v0,v1,v2,,vn} be the vertices of the fan Fn, to form the splitting graph S(Fn) we add new vertices {u0,u1,u2,,un} corresponding to the vertices of the fan Fn. The edges set of S(Fn) are {viui+1,vivi+1,uivi+1,1in1}{uiv0,viu0,viv0,1in}, the graph S(Fn) has p=2n+2 vertices and q=6n3 edges, k=max(p,q)=6n3, see Figure 5.

    Figure 5.  The splitting graph S(Fn) of the fan graph Fn.

    Case (1): When n is even, we define the labeling function f:E(S(Fn)){δ,2δ,,(6n3)δ} as follows:

    f(v0vi)={δ(n),if i=1;δ(i),if 2in1δ,if i=n
    f(uivi+1)=δ(n+i),for1in1,
    f(viui+1)=δ(2n1+i),for1in1,
    f(u0vi)={δ(3n2+i),if 1in1;δ(6n3),if i=n
    f(vivi+1)=δ(5n3i),for1in1,
    f(v0ui)=δ(6n3i),for1in.

    In view of the above labeling pattern then the induced vertex labels are:

    f(v0)=0,f(v1)=(5n2)δ,f(vn)=δ,

    f(u1)=(n)δ,f(un)=(2n2)δ,

    f(vi)=(4n3+2i)δmod[(6n3)δ],for2in1,

    f(ui)=(3n2+i)δmod[(6n3)δ],for2in1,

    Finally, f(u0)=[n1i=1f(u0vi)+f(u0vn)]mod(6n3)δ=[n1i=1(3n2+i)δ]mod(6n3)δ

    =[(7n2211n2+2)δ]mod(6n3)δ.

    If n2mod12n=12k+2

    f(u0)=[(504k2+102k+5)δ]mod(72k+9)δ=[(39k+5)δ]mod(72k+9)δ

    =[(13n64)δ]mod(6n3)δ.

    Similarly, If n0mod12n=12k then f(u0)=[(9n44)δ]mod(6n3)δ.

    If n4mod12n=12k+4 then f(u0)=[(17n84)δ]mod(6n3)δ.

    If n6mod12n=12k+6, then f(u0)=[(21n104)δ]mod(6n3)δ.

    If n8mod12n=12k+8 then f(u0)=[(n4)δ]mod(6n3)δ.

    If n10mod12n=12k+10 then f(u0)=[(5n24)δ]mod(6n3)δ.

    Case (2): When n is odd, n>3, we define the labeling function f as follows:

    f(viui+1)=δ(i),for1in1,
    f(v0ui)=δ[32(n1)+i],for1in,
    f(v0vi)=δ(9n32i),for1in.
    f(vivi+1)={δ(5n1),if i=1;δ(9n52+i2),if i=2,4,,n3,n1δ(n+i32),if i=3,5,,n4,n2
    f(uivi+1)={δ(32(n1)),if i=1;δ(6n2i),if i=2,3,,n2δ(5n12),if i=n1
    f(viu0)={δ(6n3),if i=1;δ(5n32+i),if i=2,3,,n1δ(5n2),if i=n

    In view of the above labeling pattern then the induced vertex labels are:

    f(v0)=0,f(v1)=(7n+12)δ,f(v2)=(4)δ,f(vn)=(4n1)δ,

    f(u1)=(3n2)δ,f(un1)=(6n5)δ,f(un)=(7n52)δ,

    f(vi)=(372n172+i)δmod[(6n3)δ]=(n+12+i)δ,for3in1,

    f(ui)=(15n92+i)δmod[(6n3)δ]=(3n32+i)δ,for2in2,

    Finally, f(u0)=ni=1f(u0vi)=[n1i=2f(u0vi)+f(u0v1)+f(u0vn)]mod(6n3)δ

    =[n1i=2(52n32+i)δ+(5n2)δ]mod(6n3)δ=[(3n22n)δ]mod(6n3)δ

    n1mod2n=2k+1

    f(u0)=[(12k2+8k+1)δ]mod(12k+3)δ=[(5k+1)δ]mod(12k+3)δ=(5n32)δ.

    Hence the vertex labels are all distinct and a multiple of δ. Therefore S(Fn) admits an edge δ graceful labeling.

    Illustration: The splitting graphs S(F8) with an edge 5 graceful labeling andS(F9) with an edge 4 graceful labeling are presented in Figure 6.

    Figure 6.  The graphs S(F8) with an edge 5 graceful labeling and S(F9) with an edge 4 graceful labeling.

    Theorem 2.3. For any positive integer δ, the splitting graph S(Crn) of the crown graph is an edge δ graceful graph.

    Proof. Let {v1,v2,,vn} and {u1,u2,,un} be the vertices of the crown Crn, to form the splitting graph S(Crn) we add newly vertices {v1,v2,,vn} and {u1,u2,,un} corresponding to the vertices of the crown Crn. The edges set of the splitting graph S(Crn) are {viui,vivi+1, vivi+1,vivi+1,viui,uivi,1in}, see Figure 7. The graph S(Crn) has p=4n vertices and q=6n edges, k=max(p,q)=6n.

    Figure 7.  The splitting graph S(Crn) of the crown graph.

    Case (1): When n is odd. We define the labeling function f:E(S(Crn)){δ,2δ,,(6n)δ} as follows:

    f(vivi+1)=δ(n+i),for1in,
    f(viui)=δ(5ni),for1in,
    f(uivi)=δ(6ni),for1in,
    f(vivi+1)=δ(3ni),for1in1, and f(vnv1)=δ(6n),
    f(vivi+1)=δ(3n+i),for1in1, and f(vnv1)=δ(3n),
    f(viui)={δ(n),if i=1;δ(i),if for2in1δ,if i=n

    In view of the above labeling pattern then the induced vertex labels are:

    f(u1)=nδ,f(un)=δ,f(v1)=0,f(v1)=(6n1)δ,f(vn)=(2n1)δ,

    f(ui)=(5n2i)δ,for1in,

    f(ui)=(i)δ,for2in1,

    f(vi)=(3ni+1)δ,for2in,

    f(vi)=(4n+2i2)δ,for2in1.

    Case (2): When n is even. The labeling function f:E(S(Crn)){δ,2δ,,(6n)δ} defined as follows:

    f(uivi)=δ(i),for1in,

    f(vivi+1)=δ(3n+i),for1in,

    f(vivi+1)=δ(5n+1i),for1in,

    f(v1u1)=δ(6n),f(viui)=δ(2n+1i),for2in,

    f(v1u1)=δ(6n2),f(viui)=δ(2n+i),for2in,

    f(vivi+1)={δ(5n1+2i),if 1in2δ(2n+1),if i=n2+1;δ(4n+2i2),if n2+2in1;δ(2n),if i=n.

    In view of the above labeling pattern then the induced vertex labels are:

    f(v1)=(4n+2)δ,f(vn2+1)=δ,f(vn2+2)=(5n+4)δ,f(vn)=(6n3)δ,

    f(u1)=(6n1)δ,f(u1)=0,f(v1)=(n)δ,

    f(ui)=(2n+2i)δ,for2in,

    f(ui)=(2n+1i)δ,for2in,

    f(vi)=(4n+i+2)δ,for2in,

    f(vi)=(2n+4i3)δ,for2in2,

    f(vi)=(4i5)δ,forn2+3in1.

    Hence the vertex labels are all distinct. Therefore S(Crn) admits an edge δ graceful labeling.

    Illustration: The splitting graphs S(Cr8) of the crown graph with an edge 5 graceful labeling and S(Cr9) with an edge 3 graceful labeling are shown in Figure 8.

    Figure 8.  The graphs S(Cr8) with an edge 5 graceful labeling and S(Cr9) with an edge 3 graceful labeling.

    Theorem 3.1. For any positive integer δ, the shadow graph D2(Pn),n>2 of the path Pn is an edge δ graceful graph.

    Proof. Let {v1,v2,,vn} be the vertices in first copy of Pn and {u1,u2,,un} be that in second copy of Pn. The edges set in the shadow graph D2(Pn) are {vivi+1,viui+1,uivi+1,uiui+1,1in1}. The four vertices v1,vn,u1 and un are of degree 2 and the remaining vertices are of degree 4, so the graph D2(Pn) has p=2n vertices and q=4n4 edges, k=max(p,q)=4n4.

    If n=2 the graph D2(P2) is not an edge δ graceful graph since it isomorphic to C4 [2].

    If n=3 the graph D2(P3) is an edge δ graceful graph for any positive integer δ define the labeling function f:E(D2(P3)){δ,2δ,,8δ} as shown in Figure 9.

    Figure 9.  The shadow graph D2(P3) with edge δ graceful labeling.

    If n4. We define the labeling function f:E(D2(Pn)){δ,2δ,,(4n4)δ} as follows:

    f(viui+1)=δi,for1in1,
    f(vivi+1)=δ(4n4i),for1in1,
    f(uivi+1)=δ(2ni1),for1in1,
    f(u1u2)=δ(4n4),f(u2u3)=δ(2n),f(u3u4)=δ(2n1),
    f(uiui+1)=δ(2n+i3),for4in1.

    In view of the above labeling pattern then the induced vertex labels are:

    f(v1)=0,f(vn)=δ,f(u1)=(2n2)δ,f(un)=(4n5)δ,

    f(u2)=2δ,f(u3)=(2n+1)δ,f(u4)=(2n+2)δ,

    f(vi)=[f(vivi+1)+f(vi1vi)+f(viui1)+f(viui+1)]mod[(4n4)δ]

    =(2n+12i)δ,for2in1.

    Similarly, f(ui)=(2n5+2i)δ,for5in1.

    Hence the labels of the vertices are all distinct numbers and a multiple of δ. Thus D2(Pn) is an edge δ graceful graph.

    Illustration: The shadow graph D2(P13) with edge 3 graceful labeling is presented in Figure 10.

    Figure 10.  The shadow graph D2(P13) with edge 3 graceful labeling.

    Theorem 3.2. For any positive integer δ, the shadow graph D2(Cn),n3 of the cycle Cn is an edge δ graceful graph.

    Proof. Let {v1,v2,,vn} be the vertices in first copy of Cn and {u1,u2,,un} be that in second copy of Cn. According to the construction of the shadow graph D2(Cn) of the cycle Cn, the edges set in the shadow graph D2(Cn) are {vivi+1,viui+1,uivi+1,uiui+1,i=1,2,,n}. All the vertices vi and ui are of degree 4, so the graph D2(Cn) has p=2n vertices and q=4n edges, k=max(p,q)=4n. There are two cases:

    Case (1): When n is odd, we define the labeling f:E(D2(Cn){δ,2δ,3δ,,4nδ} as follows:

    f(v1vn)=δn,f(vivi+1)=δifor1in1, f(u1un)=δ2n,f(uiui+1)=δ(n+i)for1in1, f(v1un)=δ3n,f(viui+1)=δ(4ni)for1in1, f(u1vn)=δ4n,f(uivi+1)=δ(2n+i)for1in1.

    In view of the above labeling pattern we have:

    f(v1)=nδ and f(vi)=[2δ(n+i1)]mod(4n)δ,for2in,

    f(un)=3nδ and f(ui)=(2δi)mod(4n)δ,for1in1.

    Hence the labels of the vertices v2,v3,v4,,vn1,vn are 2δ(n+1),2δ(n+2),2δ(n+3),,2δ(2n2),2δ(2n1), respectively, and the labels of the vertices u1,u2,u3,,un1,un are 2δ,4δ,6δ,,2δ(n1),3δn, respectively, which are distinct numbers.

    Case (2): When n is even, we define the labeling f as follows:

    f(uivi+1)=iδ,for1in,

    f(v1vn)=δ(4n1),f(vivi+1)=δ(2n+i),for1in1,

    f(vnu1)=δ2n,f(viui+1)=δ(4n1i),for1in1,

    f(unu1)=δ4n,f(uiui+1)=δ(n+i),for1in1.

    In view of the above labeling pattern we have:

    f(u1)=(3n+2)δ,f(un)=(2n1)δ,f(v1)=(3n2)δ,f(vn)=(2n3)δ,

    f(ui)=(2n1+2i)δmod(4n)δ,for2in1,

    f(vi)=[δ(2i3)]mod(4n)δ,for2in1.

    Obviously the vertex labels are all distinct. Thus, the graph D2(Cn) is an edge δ graceful graph for all n.

    Illustration: The shadow graph D2(C9) with an edge 5 graceful labeling and D2(C10) with an edge 3 graceful labeling are shown in Figure 11.

    Figure 11.  The shadow graph D2(C9) with an edge 5 graceful labeling and D2(C10) with an edge 3 graceful labeling.

    Theorem 3.3. For any positive integer δ, the shadow graph D2(Fn),n3 of the fan graph Fn is an edge δ graceful graph.

    Proof. Let {v0,v1,v2,,vn} be the vertices in first copy of Fn and {u0,u1,u2,,un} be that in second copy of Fn. The edges set in the shadow graph D2(Fn) are {viui+1,vivi+1,uivi+1,uiui+1,1in1}{uiv0,viu0,viv0,u0ui,1in}, so the graph D2(Fn) has number of total vertices p=|V(D2(Fn)|=2n+2 and edges q=|E(D2(Fn)|=8n4,n=2,3,4,, see Figure 12. There are three cases:

    Figure 12.  The shadow graph D2(Fn) of the fan graph Fn.

    Case (1): When n0mod4 and n2mod4, we define the labeling

    f:E[D2(Fn)]{δ,2δ,3δ,,(8n4)δ} as follows:

    f(v0vi)=δi,for1in,f(v0ui)=δ(8n4i),for1in,f(vivi+1)=δ(n+i),for1in1,f(uiui+1)=δ(3n1i),for1in1,f(viui+1)=δ(6n3i),for1in1,f(uivi+1)=δ(7n4i),for1in1,f(u0ui)=δ(4n1i),for1in,f(u0v1)=δ(8n4),f(u0vi)=δ(5n1i)for1in.

    In view of the above labeling pattern, we can check that

    (i) [f(v0vi)+f(v0ui)]mod[(8n4)δ]=0,for1in.

    (ii) [f(u0uni)+f(u0vi+2)]mod[(8n4)δ]=0,for0in2.

    Then, the induced vertex labels are:

    f(v0)=ni=1[f(v0vi)+f(v0ui)]mod[(8n4)δ]=0,

    f(u0)=ni=1[f(u0vi)+f(u0ui)]mod[(8n4)δ]=[f(u0v1)+f(u0u1)]mod(8n4)δ=(4n2)δ,

    f(v1)=(n1)δ,f(vn)=(5n)δ,f(u1)=(4n3)δ,f(un)=nδ,

    f(vi)=[f(vivi+1)+f(vi1vi)+f(viu0)+f(viv0)+f(viui+1)+f(ui1vi)]mod[(8n4)δ]

    =[δ(8n4i)]mod[(8n4)δ],for2in1.

    f(ui)=[f(uiui+1)+f(ui1ui)+f(uiu0)+f(uiv0)+f(uivi+1)+f(vi1ui)]mod(8n4)δ

    =[δ(3n2i)]mod[(8n4)δ],for2in1.

    Hence the labels of the vertices v2,v3,v4,,vn2,vn1 are δ(8n8),δ(8n12),δ(8n16),,δ(4n+8),δ(4n+4), respectively, and the labels of the vertices u2,u3,u4,,un2,un1 are δ(3n4),δ(3n6),δ(3n8),,δ(n+4),δ(n+2), respectively, which are distinct numbers.

    Case (2): When n1mod4, we define the labeling f as follows:

    f(v0vi)=δ(n1+i),for1in,f(v0ui)=δ(7n3i),for1in,f(uiui+1)=δ(4n3i),for1in1,f(u0vi)=δ(ni),for1in1,f(u0vn)=δ(4n3),f(u0ui)=δ(8n4i),for1in1,f(u0un)=δ(8n4),f(viui+1)=δ(2n1+i),for1in2,f(vn1un)=δ(4n2),f(u1v2)=δ(4n1),f(uivi+1)=δ(6n2i),for2in1,f(vivi+1)={δ(4n+i),if i=1δ(4n),if i=2δ(4n1+i),if 3in1

    In view of the above labeling pattern, the induced vertex labels are:

    f(v0)=0,f(v1)=4δ,f(v2)=8δ,

    f(v3)=δ(2n+7),f(vn1)=5nδ,f(vn)=δ,

    f(u0)=(4n3)δ,f(u1)=(7n6)δ,f(un)=(5n3)δ,

    f(vi)=[δ(2n+2+2i)]mod[(8n4)δ],for4in2.

    Finally, f(ui)=[δ(7n44i)]mod[(8n4)δ],for2in1.

    Hence the labels of the vertices v2,v3,v4,,vn2,vn1 are δ(8n8),δ(8n12),δ(8n16),,δ(4n+8),δ(4n+4), respectively, and the labels of the vertices u2,u3,u4,,un2,un1 are δ(7n12),δ(7n16),δ(7n20),,δ(3n+4),δ(3n), respectively, which are distinct numbers.

    In this labeling, the induced labeling of the vertex u0 will equal the induced labeling of the vertex

    ui when i=3n14 i.e., when n=4k+3n3mod4.

    Case (3): When n3mod4, we define the labeling f as in the case n1mod4 but we change the labeling of two edges (u0vn) and (u1v2) as follows:

    f(u0vn)=δ(4n1) and f(u1v2)=δ(4n3).

    The induced vertex labels are:

    f(v0)=0,f(v1)=4δ,f(v2)=6δ,

    f(v3)=δ(2n+7),f(vn1)=5nδ,f(vn)=3δ,

    f(u0)=(4n1)δ,f(u1)=(7n8)δ,f(un)=(5n3)δ,

    f(vi)=[δ(2n+2+2i)]mod[(8n4)δ],for4in2

    f(ui)=[δ(7n44i)]mod[(8n4)δ],for2in1.

    Hence the vertex labels are all distinct and a multiple of δ. Therefore the shadow graph D2(Fn) admits an edge δ graceful labeling.

    Illustration: The shadow graphs D2(F8) with edge 4 graceful labeling, D2(F9) with edge 3 graceful labeling and D2(F7) with an edge 5 graceful labeling. are presented in Figure 13.

    Figure 13.  Some shadow graphs D2(Fn) with distinct edge δ graceful labeling.

    Theorem 4.1. For any positive integer δ, the middle graph M(Pn) of path Pn is an edge δ graceful graph when n is even and n1mod4.

    Proof. Let {v1,v2,,vn} be the vertices and {u1,u2,,un1} be the edges of path Pn. Then V[M(Pn)]=V(Pn)E(Pn) and E[M(Pn)]={viui;1in1,viui1;2in,uiui+1;1in2}. Here p=2n1 vertices and q=3n4 edges, k=max(p,q)=3n4.

    Case (1): When n is even, We define the labeling function f:E(M(Pn)){δ,2δ,,(3n4)δ} as follows:

    f(uiui+1)={δ(n2i2),if 1in22δ(n1),if i=n21;δ(2n2i5),if n2in3;δ(n2),if i=n2.
    f(uivi)={δ(n3),if i=1δ(n+i2),if 2in1.
    f(viui1)=δ(2n4+i),for2in.

    Then the induced vertex labels are:

    f(v1)=δ(n3),f(vn)=0,f(u1)=(n5)δ,f(un1)=(3n5)δ,

    f(un2)=(3n6)δ,f(un2)=(3n7)δ,andf(un21)=(2n2)δ,

    f(vi)=[f(viui1)+f(viui)]mod[(3n4)δ]=(2i2)δ,for2in1;

    f(ui)=[f(uiiui)+f(uiui+1)+f(uivi)+f(uivi+1)]mod[(3n4)δ]

    =(2n32i)δ,for2in22, and

    f(ui)=(4n92i)δ,forn2+1i,n3.

    Case (2): When n1mod4, We define the labeling function f:E(M(Pn)){δ,2δ,,(3n4)δ} as follows:

    f(viui)=δi,for1in1,
    f(uiui+1)=δ(n+i),for1in2, and
    f(viui1)={δ(2n+i3),if 2in1δn,if i=n.

    Then the induced vertex labels are:

    f(v1)=δ,f(vn)=nδ,f(u1)=5δ,f(un1)=(n+1)δ,

    f(vi)=[f(viui1)+f(viui)]mod[(3n4)δ]=(2n3+2i)δmod[(3n4)δ]2in1,

    f(ui)=[f(uiiui)+f(uiui+1)+f(uivi)+f(uivi+1)]mod[(3n4)δ]

    =[(n+1+4i)δ]mod[(3n4)δ],for2in2.

    Hence the labels of the vertices v2,v3,,vn2,vn1 are (2n+1)δ,(2n+3)δ,,(n3)δ,(n1)δ, respectively, and the labels of the vertices u2,u3,,un3,un2 will be (n+9)δ,(n+13)δ,,(2n7)δ,(2n3)δ, respectively. Hence the vertex labels are all distinct and a multiple of δ. Therefore M(Pn) admits an edge δ graceful labeling when n is odd.

    Illustration: The middle graphs M(P14) with an edge 2 graceful labeling and M(P13) with an edge 3 graceful labeling are shown in Figure 14.

    Figure 14.  The middle graphs M(P14) with an edge 2 graceful labeling and M(P13) with an edge 3 graceful labeling.

    Theorem 4.2. For any positive integer δ, the middle graph M(Cn),n3 of the cycle Cn is an edge δ graceful graph when n is odd number.

    Proof. Let {v1,v2,,vn} be the vertices of the cycle Cn and {u1,u2,,un1} be the edges of the cycle Cn. The V[M(Cn)]=V(Cn)E(Cn) and E[M(Cn)]={uiui+1,viui,uivi+1;1in}, so the number of vertices p=|V[M(Cn]|=2n and edges q=|E[M(Cn)]|=3n,n=3,4,.

    When n is odd, we define the labeling function f:E(M(Cn)){δ,2δ,,(3n)δ} as follows:

    f(uivi+1)=δ(3i2),for1in,
    f(uiui+1)=δ(3i1),for1in,
    f(v1u1)=3nδ,f(viui)=3δ(i1),for2in.

    In view of the above labeling pattern, the induced vertex labels are:

    f(v1)=δ(3n2),f(vi)=(6i8)δmod[(3n)δ],2in,

    f(u1)=2δ,f(ui)=(12i10)δmod[(3n)δ],2in.

    Hence the vertex labels are all distinct and a multiple of δ. Therefore M(Cn) admits an edge δ graceful labeling.

    Illustration: The middle graph M(C9) of the cycle C9 with an edge 6 graceful labeling is shown in Figure 15.

    Figure 15.  The middle graph M(C9) with an edge 5 graceful labeling.

    Theorem 4.3. For any positive integer δ, the middle graph of the crown graph Crn is an edge δ graceful graph.

    Proof. Let {v1,v2,,vn} and {u1,u2,,un1} be the vertices of the crown graph Crn and v1,v2,,vn and u1,u2,,un1 be the edges of the crown graph Crn. Then V(M(Crn))=V(Crn)E(Crn) and E(M(Crn))={viui,vivi+1,vivi,uiui,uivi,viui+1,vivi+1;1in}, so p=4n vertices and q=7n edges, k=max(p,q)=7n, see Figure 16.

    Figure 16.  The middle graph M(Crn) of the crown graph Crn.

    Case (1): When n is odd, we define the labeling function f:E(M(Crn)){δ,2δ,,7nδ} as follows:

    f(vivi)=δ(n+i),for1in,
    f(vivi+1)=δ(3ni+1),for1in,
    f(viui+1)=δ(4n+i),for1in,
    f(viui)=δ(3n+i),for1in,
    f(v1u1)=δ(7n),f(viui)=δi,for2in,
    f(u1u1)=δ,f(uiui)=δ(7n+1i),for2in,
    f(vivi+1)={δ(6n2i),if 1in12δ(6n1),if i=n+12δ(7n2i),if n+32in1;δ(6n),if i=n

    Then the induced vertex labels are:

    f(v1)=(2n+1)δ,f(vn+12)=(2n+2)δ,f(vn+32)=(3n)δ,f(vn)=(3n+3)δ,

    f(v1)=(3n+2)δ,f(u1)=δ,f(u1)=(n+2)δ,

    f(vi)=(4n+i+2)δ,for2in,

    f(ui)=(7ni+1)δ,for2in,

    f(ui)=(2i)δ,for2in,

    f(vi)={δ(2n2i+3)mod[(7n)δ],if 2in12δ(4n2i+3)mod[(7n)δ],if n+52in1.

    Hence the labels of the vertices v2,v3,,vn32,vn12 are (2n1)δ,(2n3)δ,,(n+6)δ,(n+4)δ, respectively, and the labels of the vertices vn+52,vn+72,,vn2,vn1 are (3n2)δ,(3n4)δ,,(2n+7)δ,(2n+5)δ, respectively.

    Case (2): When n0mod6, and n2mod6. We define the labeling function f:E(M(Crn)){δ,2δ,,7nδ} as follows:

    f(viui)=δi,for1in,
    f(vivi+1)=δ(3ni+1),for1in,
    f(vivi)=δ(n+i),for1in,
    f(uiui)={δ(3n+1),if i=1δ(7ni+1),if 2in.
    f(uivi)={δ(7n),if i=1δ(3n+i),if 2in.
    f(viui+1)={δ(4n+1+i),if 1in1δ(4n+1),if i=n.
    f(vivi+1)={δ(5n+2i1),if 1in2δ(4n+2i),if n2+1in.

    Then the induced vertex labels are:

    f(v1)=(3n+3)δ,f(vi)=(4n+i+2)δ,for2in,

    f(u1)=(3n+1)δ,f(ui)=(7ni+1)δ,for2in,

    f(u1)=3δ,f(ui)=(2i+1)δ,for2in,

    f(v1)=(5n+4)δ,f(vn2+1)=(2n+5)δ,f(vn)=(3n)δ and

    f(vi)={δ(6i2)mod[(7n)δ]if 2,in2δ(5n+6i)mod[(7n)δ]if n2+2in1.

    Hence the labels of the vertices v2,v3,,vn21,vn2 are 10δ,16δ,,(3n8)δ,(3n2)δ, respectively, and the labels of the vertices vn2+2,vn2+3,,vn2,vn1 are (n+12)δ,(n+18)δ,,(4n12)δ,(4n6)δ, respectively.

    We notice that, these values are distinct for all n even except when n4mod6, since

    vn2+2=(n+12)δ=v3=16δ,whenn=4

    vn2+2=(n+12)δ=v4=22δ,whenn=10

    vn2+2=(n+12)δ=v5=28δ,whenn=16

    Case (3): When n4mod6. Define the labeling function f:E(M(Crn)){δ,2δ,,7nδ} as in the first case with changes in the following edges

    f(vivi+1)={δ(5n+2i),if 1in2δ(4n+2i1),if n2+1in.

    Then the induced vertex labels are:

    f(v1)=(5n+4)δ,f(vn2+1)=(2n+5)δ,f(vn)=(3n2)δ and

    f(vi)={δ(6i)mod[(7n)δ]if 2in2δ(5n+6i2)mod[(7n)δ]if n2+2in1.

    Hence the labels of the vertices v2,v3,,vn21,vn2 are 12δ,18δ,,(3n6)δ,(3n)δ, respectively, and the labels of the vertices vn2+2,vn2+3,,vn2,vn1 are (n+10)δ,(n+16)δ,,(4n14)δ,(4n8)δ, respectively. Hence there are no repetition in the vertex labels which completes the proof.

    Illustration: The middle graphs M(Cr10) with an edge 3 graceful labeling and M(Cr9) with an edge 2 graceful labeling are shown in Figure 17.

    Figure 17.  The middle graphs M(Cr10) with an edge 3 graceful labeling and M(Cr9) with an edge 2 graceful labeling.

    Theorem 5.1. For any positive integer δ, the total graph T(Pn) of the path Pn is an edge δ graceful graph.

    Proof. Let {v1,v1,,vn} be the vertices of the path Pn, the total graph T(Pn) of path Pn has vertices set V(T(Pn))={vi,1in}{ui,1in1} and edges set E(T(Pn))={vivi+1,viui,uivi+1,1in1}{uiui+1,1in2}, so the graph T(Pn) has p=2n1 and q=4n5, k=max(p,q)=4n5.

    If n=2 the graph T(P2) is an edge δ graceful graph since it isomorphic to C3 [15]. There are two cases:

    Case (1): When n is even, n4. We define the labeling function f:E(T(Pn)){δ,2δ,,(4n5)δ} as follows:

    f(viui)=δi,for1in1, $
    f(vivi+1)=δ(n1+i),for1in1,
    f(uivi+1)=δ(4n5i),for1in1,
    f(uiui+1)={δ(4n5),if i=1δ(2n3+i),if 2in2

    In view of the above labeling pattern then the induced vertex labels are:

    f(v1)=(n+1)δ,f(vn)=(n1)δ,f(u1)=0,f(u2)=(2n1)δ,f(un1)=(3n5)δ,

    f(vi)=[(2n2+2i)δ]mod[(4n5)δ],for2in1,

    f(ui)=(2i2)δ,for3in2.

    Hence the labels of the vertices are all distinct numbers.

    Case (2): When n is odd:

    If n=3 the graph T(P3) is an edge δ graceful graph for any positive integer δ define the labeling function f:E(T(P3)){δ,2δ,,7δ} as shown in Figure 18.

    Figure 18.  The total graph T(P3) with edge δ graceful labeling.

    If n5. Define the labeling function f:E(T(Pn)){δ,2δ,,(4n5)δ} as follows:

    f(viui)=δi,for1in1,
    f(uiui+1)=δ(2n2+i),for1in2,
    f(uivi+1)=δ(2n1i),for1in1, and
    f(vivi+1)={δ(4n5),if i=1;δ(3n4+i),if 2in2δ(3n3),if i=n1

    In view of the above labeling pattern then the induced vertex labels are:

    f(v1)=δ,f(v2)=(n+3)δ,f(vn1)=(n+1)δ,

    f(vn)=2δ,f(u1)=3δ,f(un1)=nδ,

    f(vi)=[(1+2i)δ]mod[(4n5)δ],for3in2, and

    f(ui)=[(2n1+2i)δ]mod[(4n5)δ],for2in2.

    Hence the labels of the vertices v3,v4,,vn3,vn2 will be 7δ,9δ,,(2n5)δ,(2n3)δ, respectively, and the labels of the vertices u2,u3,,un3,un2 will be (2n+3)δ,(2n+5)δ,,(4n7)δ,0, respectively.

    In this case we have f(vn12) will equal f(un1), so we change the labeling of two edges (vn52vn32) and (vn32vn12) as follows f(vn52vn32)=δ2(7n11). and f(vn32vn12)=δ2(7n13).

    Then f(vn52)=(n3)δ and fvn12=(n1)δ Hence the vertex labels are all distinct and a multiple of δ. Therefore T(Pn) admits an edge δ graceful labeling.

    Illustration: The total graphs T(P10) and T(P11) with an edge 6 graceful labeling are shown in Figure 19.

    Figure 19.  The total graphs T(P10) and T(P11) with an edge 6 graceful labeling.

    Theorem 5.2. For any positive integer δ, the total graph T(Cn),n3 of the cycle Cn is an edge δ graceful graph.

    Proof. Let {vi,i=1,2,,n} be the vertices of the path Cn, the total graph T(Cn) of path Cn has vertices set V(T(Cn))={vi,ui,i=1,2,,n} and E(T(Cn))={vivi+1,viui,uivi+1,uiui+1,i=1,2,,n}, so the graph T(Cn) has p=2n and q=4n, k=max(p,q)=4n. There are two cases:

    Case (1): When n is even, we define the labeling f:E(T(Cn){δ,2δ,3δ,,4nδ} as follows:

    f(vivi+1)=δ(n+i),for1in,f(uivi)=δ(4ni),for1in,f(u1un)=δ4n,f(uiui+1)=δi,for1in1,f(v1un)=δn,f(uivi+1)=δ(2n+i),for1in1,

    In view of the above labeling pattern we have:

    f(v1)=0,f(u1)=(2n+1)δ,f(un)=(n1)δ,

    f(vi)=2δ(i1),for2in,

    f(ui)=δ(2i+2n1),for2in1.

    Hence the labels of the vertices v2,v3,v4,,vn1,vn are 2δ,4δ,6δ,,2δ(n2),2δ(n1), respectively, and the labels of the vertices u2,u3,u4,,un2,un1 are δ(2n+3),δ(2n+5),δ(2n+7),,δ(4n5),δ(4n3), respectively.

    It is easy to see that: f(un)=f(vi) when i=n+12, but n is even number, so all the labels are distinct numbers.

    Case (2): When n is odd, we define the labeling f as in the above case where n is even but we change the labeling of two edges (unv1) and (vnv1) as follows f(unv1)=2nδ and f(vnv1)=nδ.

    The induced vertex labels are:

    f(v1)=[f(v1v2)+f(vnv1)+f(u1v1)+f(unv1)]mod(4n)δ=0,

    f(vn)=[f(vnv1)+f(vn1vn)+f(unvn)+f(un1vn)]mod(4n)δ=δ(n2),

    f(un)=[f(unu1)+f(un1un)+f(unv1)+f(unvn)]mod(4n)δ=(2n1)δ.

    It is easy to see that: f(vn)=f(vi) when i=n2, but n is odd number, so all the labels are distinct numbers.

    Illustration: The total graph T(C10) of the cycle C10 with an edge 5 graceful labeling and the total graph T(C9) of the cycle C9 with an edge 6 graceful labeling are shown in Figure 20.

    Figure 20.  The total graph T(C10) with an edge 5 graceful labeling and T(C9) with an edge 6 graceful labeling.

    Theorem 5.3. For any positive integer δ, the total graph of the crown graph Crn is an edge δ graceful graph.

    Proof. Let {v1,v2,,vn} and {u1,u2,,un} be the vertices of the crown graph Crn and {v1,v2,,vn} and {u1,u2,,un} be the edges of the crown graph Crn. Then V(T(Crn))=V(Crn)E(Crn) and E(T(Crn))={viui,vivi+1,vivi,uiui,uivi,viui+1,vivi+1,viui,vivi+1;1in}, see Figure 21.

    Here p=4n vertices and q=9n edges, k=max(p,q)=9n.

    Figure 21.  The total graph T(Crn) of the crown graph.

    Case (1): When n is odd. Define the labeling function f:E(T(Crn)){δ,2δ,,9nδ} as follows:

    f(viui)={δ(n+1),if i=1δi,if 2in.
    f(uiui)=δ(2n+2i),for1in,
    f(viui)={δ(3n+1),if i=1δ(2n+i),if 2in.
    f(vivi)={δ,if i=1δ(3n+i),if 2in.
    f(vivi+1)=δ(4n+i),for1in,
    f(vivi+1)=δ(5n+i),for1in,
    f(vivi+1)={δ(7ni),if 1in1δ(7n),if i=n
    f(viui+1)=δ(7n+i),for1in,
    f(viui)=δ(9n+1i),for1in.

    Then the induced vertex labels are:

    f(v1)=(8n+3)δ,f(vi)=(8n+4i1)δmod[(9n)δ],for2in,

    f(u1)=(5n+3)δ,f(ui)=(2n+2i+1)δ,for2in,

    f(ui)=(2n+32i)δ,for1in,

    f(v1)=(n+3)δ,f(vn)=(6n+1)δ,f(vi)=(3n+1+2i)δ,for2in1.

    Case (2): When n2mod4. The labeling function f:E(T(Crn)){δ,2δ,,9nδ} defined as follows:

    f(uiui)=δ(i),for1in,
    f(uivi)=δ(n+i),for1in,
    f(viui)=δ(2n+i),for1in,
    f(vivi+1)=δ(3n+i),for1in,
    f(vivi+1)=δ(5n+1i),for1in,
    f(vivi+1)=δ(5n+i+1),for1in1,f(vnv1)=δ(5n+1),
    f(vivi)=δ(6n+i),for1in,
    f(viui+1)=δ(7n+i),for1in,
    f(viui)=δ(8n+i),for1in.

    Then the induced vertex labels are:

    f(ui)=(8n+2i)δmod[(9n)δ],for1in,

    f(u1)=(2n+3)δ,f(ui)=(n+4i1)δ,for2in,

    f(vi)=(8n+4i+1)δmod[(9n)δ],for1in,

    f(v1)=(3n+6)δ,f(vn)=(6n+2)δ,f(vi)=(3n+2+4i)δ,for2in1.

    These values are distinct for all n2mod4, but

    f(vi)=(3n+4i+2)δ=f(vn)=(6n+3)δ, when i=3n4 i.e., when n0mod4.

    Case (3): When n0mod4 define the labeling function f as follows:

    f(uiui)=δ(i),for1in,
    f(uivi)=δ(n+i),for1in,
    f(vivi+1)={δ(3n+i),if 1in1δ(2n+1),if i=n
    f(viui)={δ(4n),if i=1;δ(2n+i),if 2in
    f(vivi+1)=δ(5n+1i),for1in,
    f(vivi+1)=δ(5n+i),for1in,
    f(vivi)=δ(6n+i),for1in,
    f(viui+1)=δ(7n+i),for1in,
    f(viui)=δ(8n+i),for1in.

    Then the induced vertex labels are:

    f(ui)=(8n+2i)δmod[(9n)δ],for1in,

    f(u1)=(4n+2)δ,f(ui)=(n+4i1)δ,for2in,

    f(v1)=(6n+3)δ,f(vi)=(3n+4i)δ,for2in,

    f(v1)=(6n+6)δ,f(vn)=(n+2)δ,

    f(vi)=(8n+4i+1)δmod[(9n)δ],for2in1.

    We notice that, these values are distinct for all n0mod4. It should be notice that:

    f(vi)=(3n+4i)δ=f(u1)=(4n+2)δ, when i=n+24 i.e., when n2mod4. Hence there are no repetition in the vertex labels which completes the proof.

    Illustration: The total graphs T(Cr8) and T(Cr9) of the crown graph with an edge 3 graceful labeling are shown in Figure 22.

    Figure 22.  The total graphs T(Cr8) and T(Cr9) of the crown graph with an edge 3 graceful labeling.

    Definition 6.1. The twig graph TWn,n4 is the graph obtained from path Pn={v1,v2,,vn} by attaching exactly two pendant edges to each internal vertex of the path Pn.

    Theorem 6.1. For any positive integer δ, the twig graph TWn is an edge δ graceful graph when n is odd.

    Proof. Let {v1,v2,,vn} be the vertices of the path Pn and the new attaching vertices are {u2,u3,,un1} and {w2,w3,,wn1}. The edges of TWn are denoted by {ai,bi,ci,di}, where ai={v(n4i+32)v(n4i+52)}, bi={v(n+4i32)v(n+4i12)}, di={v(n4i+12)v(n4i+32)} and ci={v(n+4i12)v(n+4i+12)} where,

    i={1,2,,n14if i1mod4;1,2,,n+14if i3mod4

    The graph TWn has p=3n4 vertices and q=3n5 edges, k=max(p,q)=3n4. see, Figure 23 We define the labeling function f:E(TWn){δ,2δ,,(3n4)δ} as follows:

    Figure 23.  The twig graph TWn with ordinary labeling.

    At the beginning, we determine the middle vertex vn+12 in the path Pn and we start the labeling from this vertex by using the following algorithm.

    First step: Label the edges a1,b1,c1 and d1 in the following order:

    f(a1)=δ, f(b1)=δ(3n5), f(c1)=2δ and

    f(d1)=[f(b1)f(a1)]mod[δ(3n4)]=δ(3n6).

    Second step: Label the vertices ai,bi,ci and di by the following algorithm respectively

    (i) f(ai)=[f(ci1)f(di1)]mod[δ(3n4)],  for  i=2,3,,n34,

    (ii) f(bi)=(3n4)δf(ai),

    (iii) f(ci)=[f(ai)f(bi)]mod[δ(3n4)],  for  i=2,3,,n74,

    (iv) f(di)=[f(bi)f(ai)]mod[δ(3n4)].  for  i=2,3,,n74,

    and repeats the second step until we fish the labeling of all edges in the path Pn.

    At the end, the edges (viui) and (viwi),2in1 take any number from the reminder set of the labeling such that [f(viui)+f(viwi)]mod[δ(3n4)]0mod[δ(3n4)]fori=2in1.

    In view of the above labeling algorithm, the labels of the vertices are,

    f(vn+12)=[f(a1)+f(b1)+f(un+12)+f(wn+12)]mod[δ(3n4)]=0,

    f(vn12)=f(b1)=δ(3n5),f(vn+32)=f(a1)=δ,

    f(vn32)=f(c1)=2δ,f(vn+52)=f(d1)=δ(3n6),

    f(vn52)=f(b2)=δ(3n8),f(vn+72)=f(a2)=4δ,

    f(vn+(4i1)2)=f(ai),f(vn(4i3)2)=f(bi),  for  i=1,2,,n14,

    f(vn+(4i+1)2)=f(di),f(vn(4i1)2)=f(ci),  for  i=1,2,,n54.

    The pendant vertices v1andvn of the path Pn will take the labels of its pendant edges, i.e.,

    If n1(mod4), then f(v1)=f(dn14),  and   f(v2n1)=f(cn14).

    If n3(mod4), then f(v1)=f(an+14),  and   f(vn)=f(bn+14).

    It is clear that the labels of the vertices of the path Pn take the labels of the edges of the path and each pendant vertex takes the labels of its incident edge. Then there are no repeated vertex labels, which completes the proof.

    Illustration: The twig graph TW13 is presented in Figure 24 with an edge 4 graceful labeling.

    Figure 24.  The twig graph TW13 with an edge 4- graceful labeling.

    Definition 7.1. A snail graph Sn is obtained from path Pn={v1,v2,,vn} by attaching two parallel edges between vi and vni+1 for i=1,2,,n2.

    Theorem 7.1. For any positive integer δ, the snail graph Sn, n>2 is an edge δ graceful graph.

    Proof.

    Case (1): When n is even, the vertices of the graph Sn are {v0,v1,v2,,vn} and the edges are {e1,e1,,en1,a1,a2,an2,b1,b2,bn2} where {ei=vivi+1,i=1,2,,n1} and {aj=bj=vivni+1,j=1,2,,n2}, see Figure 25, in this case p=n,q=2n1 and k=max(p,q)=2n1.

    Figure 25.  The sinal graph Sn with ordinary labeling when n is even.

    We define the labeling function f:E(Sn)){δ,2δ,,(2n1)δ} as follows:

    f(ai)=δi,for1in2,f(bi)=δ(2ni1),for1in2,f(ei)={δ(i+n2),if 1in21δ(2n1),if i=n2δ(n2+i1),if n2+1in1

    The induced vertex labels are:

    f(v1)=[f(a1)+f(b1)+f(e1)]mod[(2n1)δ]=δ[n2+1],

    f(vn)=[f(a1)+f(b1)+f(en1)]mod[(2n1)δ]=δ[3n22],

    f(vn2)=δ(n1),f(vn2+1)=δn.

    f(vi)=[f(ai)+f(bi)+f(ei)+f(ei1)][mod(2n1)δ]

    ={δ(n+2i1)mod[(2n1)δ]if 2in21;δ(n+2i3)mod[(2n1)δ]if n2+2in1.

    Hence the labels of the vertices v2,v3,,vn21 are δ(n+3),δ(n+5),,δ(2n3), respectively, and the labels of the vertices vn2+2,vn2+3,,vn1 are 2δ,4δ,,δ(n4), respectively.

    Note that S4 is an edge δ graceful graph but not follow this rule, see Figure 26.

    Figure 26.  The sinal graph S4 with an edge δ labeling.

    Case (2): When n is odd. Let {e1,e1,,en1,a1,a2,,an12,b1,b2,bn12} be the edges of Sn which are denoted as in the Figure 27, in this case p=n,q=2n2,k=max(p,q)=2n2.

    Figure 27.  The snail graph Sn with ordinary labeling when n is odd.

    Define the labeling function f:E(Sn)){δ,2δ,,(2n2)δ} as follows:

    f(ei)=iδ,for1in1,f(ai)=δ(n+i1),for1in12,f(bi)=δ(2ni1),for1in12.

    Therefor, the induced vertex labels are

    f(v1)=δ(n+1),f(vn+12)=nδ,f(vn)=δ and

    f(vi)=[f(ai)+f(bi)+f(ei)+f(ei1)]mod[(2n2)δ]

    =δ(n+2i1)mod[(2n2)δ],ifi=2,3,,n12,n+22,,n1.

    Hence the labels of the vertices v2,v3,,vn32,vn12 are δ(n+3),δ(n+5),,δ(2n4),0, respectively, and the labels of the vertices vn+32,vn+52,,vn2,vn1 are 4δ,6δ,,(n3)δ,(n1)δ, respectively. Overall all vertex labels are distinct and a multiple of δ numbers. Hence, the snail graph Sn is an edge δ graceful for all n.

    Illustration: In Figure 28, we present a triple graceful labeling of the graph S12 and an edge 4 graceful labeling of S13.

    Figure 28.  An edge 3 graceful labeling of S12 and an edge 4 graceful labeling of S13.

    Recently, edge graceful labeling of graphs has been studied too much and these objects continue to be an attraction in the field of graph theory and discrete mathematics. A senior number of published papers and results exist. So far, numerous graphs are unknown if it is edge graceful or not.

    In this work, we pushed the new type of labeling (edge δ graceful labeling), by finding more graphs that have edge δ graceful labeling. We prove the existence of an edge δ graceful labeling, for any positive integer δ, for the following graphs. The splitting graphs of the cycle, fan, and crown graphs. The shadow graphs of the path, cycle, and fan graphs. The middle graphs and the total graphs of the path, cycle, and crown graphs. Finally, we display the existence of an edge δ graceful labeling, for the twig and snail graphs.

    The authors declare that they have no competing interests.



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