Gauss's Lemma (Ring Theory)
From ProofWiki
Theorem
Let $R$ be a unique factorization domain.
Then the Ring of Polynomial Functions $R \left[{X}\right]$ is a unique factorization domain.
Proof
Since a UFD is Noetherian, and a Noetherian Domain is UFD if every irreducible element is prime, it is sufficient to prove that every irreducible element of $R[X]$ is prime.
etc,
$\blacksquare$