I am working on a proof to show that two open intervals (a, b) such that a<b and (c,d) such that c<d are equinumerous. To do so I know that I need to show a bijection between the two, but am having difficulty coming up with a function that I can prove is a bijection.

The first part of the problem asks to come up with a bijection mapping (0,1) onto (m,n) where m<n. Maybe if someone would be kind enough to give that example I could then find a general case.

Thanks in advance.