they look identical. so what now? there's another rule we can apply.
the rule states that a "p ⊃ q" argument is the same as a "~p v q" argument where "v" means "or"
so we can turn N ⊃ ~N into ~N v ~N
this type of statement where the two sides of a proposition are the same is known as a "tautology." and a tautology can always be simplified to it's sole part, which in this case is ~N, which is "I have zero nickels."
So if he had one nickel, he indeed would have zero nickels.