Eisenstein's criterion

Statement

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

$f(x)=r_0{x}^n+r_1{x}^{n-1}+\dots +r_{n-1}x+r_n$

where $r_0\notin P$, $r_1,r_2,\dots ,r_n\in P$ and $r_n\notin P^2$, then $f$ is an irreducible polynomial.