如果可以给图G的边用集合(±1,±2,.. ,±k)中的元素标号,使得对G每个顶点u,其标号,即所有与其相邻的边的标号之和,都落在集合(±1,±2,.. ,±k)中,且Ie(i)-e(-i)I≤1和lu(i)-u(-i)1≤1,其中t心)和e(i)(1≤i≤k)分别是标号为i的顶点数和边数,那么就称该图G为Hk-cordial的.本文证明了除了尥以外,每棵树都是H3-cordial的.
A graph G is called to be Hk-cordial, if it is possible to label the edges with the numbers from the set {±1,±2,.. ,±k} in such a way that, at each vertex v, the label of it, that is the algebraic sum of the labels on the edges incident with v, is in the set {±1,±2,.. ,±k} and the inequalities |e(i)-e(-i)|≤1 and |v(i)-v(-i)≤1 are also satisfied for each i with 1≤0≤k,where v(i) and e(i) are, respectively, the numbers of vertices and edges labeled with i. In the paper, every tree is shown to be H3-cordial, except the complete graph K2.