Theorem 4.1 An edge e of a graph G is a bridge if and only if e lies on no cycle of G 推论：Every edge in a tree is a bridge 问题1： 从应用的角度看，上述推论有何 指导意义？Theorem 4.1 An edge e of a graph G is a bridge if and only if e lies on no cycle of G. 推论：Every edge in a tree is a bridge