5Path- a path of length m is a sequence(序列)ofm distinct branches together with m+l distinct nodes such that every node is of degree 2 except the initial and terminal nodes, which are of degree 1 6. Loop--A loop of length m is a path such that its initial and terminal nodes coincide(重合) 7. Connected(连通) Graph- a graph g is said to be connected if there is least one path between any two of this nodes5. Path-- A path of length m is a sequence (序列)of m distinct branches together with m+1 distinct nodes such that every node is of degree 2 except the initial and terminal nodes, which are of degree 1. 6. Loop--A loop of length m is a path such that its initial and terminal nodes coincide（重合）. 7. Connected（连通） Graph--A graph G is said to be connected if there is least one path between any two of this nodes