Question

If U and V are open, is uUv? What about u intersect v?

Answer 1

i assume you mean intervals?

Answer 2

(------------)
a b
(-----------------)
c d
****************************
(----------------------)
a d

or if we interesect them ... what do they have in common?

(----) U (----) U (-------)
a c c b b d

Answer 3

don't you just hate talking to a wall? :3

Answer 4

lol, i have teenagers now so im used to it

Answer 5

I believe the question is about open sets in general. The answer is both is yes.