>See, I told you I was ignorant!
>I see it now:
> If they are both subsets
> of each other, then they
> are equal.
This has absolutely nothing to do with ignorance, au contraire! You "dared" to ask something about a detail you have never really heard of, and that is *exactly* the best way to learn new things, studying the information that is available and in case something is not 100% clear then asking questions to clarify. I think this is absoulutely the best attitude people can possibly have!