I am stumped by an exercise in Bondy’s book:
Show that every graph has an edge cut $[X,Y]$ such that $G[X]$ and $G[Y]$ are even.
I tried many ideas, such as making induction on the number of edges, considering how to adjust the old edge cut after removing an edge and then putting it back, or taking out a circle and then putting it back, but without exception, there were always uncontrollable vertices that could not be discussed.. Could you please give me some answers or tips? Thanks a lot!:)