I'm reading the wikipedia article on 'well-founded relation', and this is the beginning part of it:
In mathematics, a binary relation, R, is well-founded on a class X if and only if every non-empty subset of X has a minimal element with respect to R
I am very, very new to set-theory (as in, I started reading about it an hour ago), so I'm reading articles on wikipedia and 'backtracking' if I don't know what a certain definition means, until I can finally understand an article properly.
Here I didn't exactly know what a 'class' is, and I found out that it is a collection of sets which can be defined by a property all of its members share.
But the wikipedia article talks about a subset of X? What does this mean? I'm guessing it means either:
A bunch of sets
A subset of every set of the class