Recent content by x_saved_kt

Ah, I see. Thanks, this makes a lot of sense now! I guess all I was thinking is that if in the question they indicated the "if"s I've got to be doing something wrong! hah! Thanks a lot for your help!

This is the question: Let A be an open set and B a closed set. If B ⊂ A, prove that A \ B is open. If A ⊂ B, prove that B \ A is closed. Right before this we have a theorem stated as below: In R^d, (a) the union of an arbitrary collection of open sets is open; (b) the intersection of any...