Eisenstein's criterion

Statement

Let $R$ be an integral domain and $P$ a prime ideal in $R$. Consider a primitive polynomial:

$f(x)=r_{0}x^{n}+r_{1}x^{n-1}+\ldots +r_{n-1}x+r_{n}$

where $r_{0}\notin P$, $r_{1},r_{2},\ldots ,r_{n}\in P$ and $r_{n}\notin P^{2}$, then $f$ is an irreducible polynomial.