It is considered impossible to prove a definition.
If the above is not given as the definition of isomorphic graphs, then how does your textbook define isomorphic graphs?
I'm having difficulty with this proof since I'm not sure how the two iffs affect the layout of the solution:
Show that two simple graphs and are isomorphic if and only if there is a bijection such that if and only if .
Any help would be much appreciated,
Ultros