For each of the pairs $G_1, G_2$ of the graphs in figures below, determine (with careful explanation) whether $G_1$ and $G_2$ are isomorphic.
For figure (a), two graphs have the same number of vertices and edges. They also have the same degree sequences. But, from this information we still can't conclude that they are isomorphic. Likewise the graphs in figure (b). So, what should I do to determine whether two graphs are isomorphic or not?