An m-restricted edge cut is an edge cut that separates a connected graph into a disconnected one with no components having order less than m. m-restrict edge connectivity λm is the cardinality of a minimum m-restricted edge cut. Let G be a connected k-regular graph of order at least 2m that contains m-restricted edge cuts and X be a subgraph of G. Let θ(X) denote the number of edges with one end in X and the other not in X and ξm=min{θ(X) ;X is a connected vertex-induced subgraph of order m}.It is proved in this paper that if G has girth at least m/2+2,then λm≤ξm.The upper bound of λm is sharp.
A restricted edge cut is an edge cut of a connected graph whose removal resultsin a disconnected graph without isolated vertices. The size of a minimum restricted edge cutof a graph G is called its restricted edge connectivity, and is denoted by λ′(G). Let ξ(G) bethe minimum edge degree of graph G. It is known that λ′(G) ≤ξ(G) if G contains restrictededge cuts. Graph G is called maximal restricted edge connected if the equality holds in thethe preceding inequality. In this paper, undirected Kautz graph UK(2, n) is proved to bemaximal restricted edge connected if n ≥ 2.
OU Jian-pingDepartment of Mathematics, Shantou University, Shantou 515063, China
设 S 是 n 项可图序列, σ(S) 是 S 中的所有项之和, 设 H 是一个简单图, σ(H,n)是使得任意 n 项可图序列满足 σ(S) ≥ m , 则 S 有一个实现包含 H 作为子图的 m 的最小值, 本文给出了 σ(K p,1,1,...,1,n) 的下界并猜测对于所有的 n ≥ (t2 ) + 3p 此下界是可达到的.
