thanks, it helps a lot, but in doing so, i still need to prove that the intersection of 2 regions is a region, which i haven't proved it yet, would you give me a hand on that?
i just ran into a hard problem, may be any of you guy can help...
prove that if the point p is a limit point of H U K where H and K are point sets, then p is a limit point of H or p is a limit point of K.
Given definition of a limit point is: a point p is said to be a limit point of a point...