Eisenstein's criterion

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

$$f(x) = r_0x^n + r_1x^{n-1} + \ldots + r_{n-1} x + r_n$$

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.