# Math Help - one one mapping

1. ## one one mapping

Mapping f: N --> N is defined by f(n)=n-(-1)n . How to show that f is one-one?

2. ## Re: one one mapping

Hi,
As usual assume f(n) = f(m) and show n = m. To do this first show from f(n) = f(m) that it is impossible that one of n, m is even and the other is odd. Then finish it up.