Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2023/iii/paper-101/4/c/solution

Suppose first that is a unique factorization domain, and let be a minimal nonzero prime ideal. Choose and factor it into irreducibles. In a UFD each irreducible is a prime element, so one factor belongs to . The nonzero prime ideal must equal by minimality.
Conversely, the ascending chain condition in the Noetherian domain implies that every nonzero nonunit factors into irreducibles. Let be irreducible and choose a prime minimal over . The Krull principal ideal theorem gives . Since is a domain and , it is a minimal nonzero prime and hence is principal, say . The divisibility and irreducibility of force to be associate to , so is prime. Thus every irreducible is prime, proving that is a UFD. This is the Minimal-prime criterion for a Noetherian unique factorization domain.

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