关于block的几个理解 Theorem 5.7 A graph of order at least 3 is nonseparable if and only if every two vertices lie on a common cycle. x u Uk-1 Uk=U 问题4：从这个定 理及证明中能否 看出，非分离图 在外表上具有什 么共性？
关于block的几个理解 Theorem 5.7 A graph of order at least 3 is nonseparable if and only if every two vertices lie on a common cycle. 问题4：从这个定 理及证明中能否 看出，非分离图 在外表上具有什 么共性？
关于block的几个理解 A maximal nonseparable subgraph of a graph G is called a block of G 极大还是 最大？
关于block的几个理解 A maximal nonseparable subgraph of a graph G is called a block of G. 极大还是 最大？
关于block的几个理解 Theorem 5.8 Let R be the relation defined on the edge set of a nontrivial connected graph G by e R f,where e,f eE(G),if e f or e and f lie on a common cycle of G.Then R is an equivalence relation. 用等价关系来描述边之间的关系，到底有何用意？ Each subgraph of G induced by the edges in an equivalence class is in fact a block of G 问题6：Bock的“极大”特性，是否能够被“等价 类”保证？
关于block的几个理解 Theorem 5.8 Let R be the relation defined on the edge set of a nontrivial connected graph G by e R f, where e, f ∈E(G), if e = f or e and f lie on a common cycle of G. Then R is an equivalence relation. 用等价关系来描述边之间的关系，到底有何用意？ Each subgraph of G induced by the edges in an equivalence class is in fact a block of G. 问题6：Block的“极大”特性，是否能够被“等价 类”保证？
问题7： 两个block的“边界”是什么？ Corollary 5.9 Fvery two distinct blocks B and B in a nontrivial connected graph G have the following properties: (a) The blocks B and B are edge-disjoint. (b)The blocks B and B have at most one vertex in common. (c)If B and B,have a v vertex v in common, then v is a cut-vertex of G
Corollary 5.9 Every two distinct blocks B1 and B2 in a nontrivial connected graph G have the following properties: (a) The blocks B1 and B2 are edge-disjoint. (b) The blocks B1 and B2 have at most one vertex in common. (c) If B1 and B2 have a vertex v in common, then v is a cut-vertex of G