If be three cardinals. Prove that .

Thoughts...

My basic problem is that I have never really understood how to construct in/sur/bijections so all this cardinal number stuff is proving to be a bit hard...

But my thoughts on this are that...

Let be the cardinal numbers of the sets A,B and C respectively such that B and C are disjoint. Then and are disjoint and .

I'm not sure whether I'm allowed to assume the disjoint part and how to construct a bijection between the two...