LET XY be subsets of R. Prove that XUY = XUY and that xny c x n y

26. Let and. Prove that for any subset of T of .

Prove that the cancellation law for multiplication holds in Z. That is, if xy=xz and x0, then y=z.

6. For the given subsets and of Z, let and determine whether is onto and whether it is one-to-one. Justify all negative answers. a. b.