I was working from the famous book of Deo. Then i found this problem very hard and interesting. Any ideas to give me?

- βLet us define a new term called edge isomorphism as follows: Two graphs G1 and G2 are edge isomorphic if there is a one-to-one correspondence between the edges of G1 and G2 such that two edges are incident (at a common vertex) in G1 if and only if the corresponding edges are also incident in G2. Discuss the properties of edge isomorphism. Construct an example to prove that edge-isomorphic graphs may not be isomorphic.β