设G是一个图,n,k和d是三个非负整数,满足n+2k+d≤|V(G)|-2,|V(G)|和n+d有相同的奇偶性.如果删去G中任意n个点后所得的图有k-匹配,并且任-k-匹配都可以扩充为一个亏d-匹配,那么称G是一个(n,k,d)-图.Liu和yu首先引入了(n,k,d)-图的概念,并且给出了(n,k,d)-图的一个刻划和若干性质.(0,k,1).图也称为几乎k-可扩图.在本文中,作者改进了(n,k,d)-图的刻划,并给出了几乎k-可扩图和几乎k-可扩二部图的刻划,进而研究了几乎k-可扩图与n-因子临界图之间的关系.
Let G be a graph, and let n, k and d be three nonnegative integers such that n+2k+ d ≤ |V(G) | - 2 and, |V(G) | and n + d have the same parity. If after deleting any n vertices from G the remaining subgraph of G contains an k-matching and each k-matching of the subgraph can be extended to a defect-d-matching of the subgraph, then G is called an (n, k, d)-graph. Liu and Yu first introduced (n, k, d)-graphs, and gave some properties and characterization of (n, k, d)-graphs. A (0, k, 1)-graph may be also called a near k-extendable graph. In the present paper, the authors improve the characterization of (n, k, d)-graphs, and consequently obtain a characterization of near k-extendable graphs. Furthermore, a characterization of near k-extendable bipartite graphs and the relations between near k-extendable graphs and n-factor critical graphs are investigated.