Hello p00ndawgYou're kind of on the right track, but you're not using the notation correctly. So let me start you off.

As you say, we need to prove that each set is a subset of the other, in order to prove they're equal. So let's prove first that . We do this by choosing an element in the first set, and showing that it's also in the second.

So let's suppose that . That means that there's an for which .

Now

But and

So

So we've just proved that . In other words, that

OK? Now you've got to prove it the other way round. Start with and ...

Grandad