Prove that R ⊂ X x Y is a bijection between the sets X and Y, when R−1R= I: X→X and RR-1=I: Y→Y Set theory is a quite a new lesson for me. So I am not good at proving different connections, but please give me a little help with what to start and so.. I have read the book and I know what bijection means but just.. I would be very very thankful. Getting a good example proof or just some tips what to do would improve my skills also I hope :) Thank you in advance!