Past exam of the commutative algebra course of the University of Oxford 2023 1 b ii Solution 2026-10-25
In the terminology of a minimal primary decomposition, an associated prime of a primary decomposition of is a prime ideal occurring as in such a decomposition. The first uniqueness theorem for primary decomposition says that this collection is independent of the chosen minimal primary decomposition. Among these prime ideals, an isolated prime of a primary decomposition is minimal under inclusion, equivalently a minimal prime over an ideal ; an embedded prime ideal strictly contains another member of the collection. ThusWhen is a Noetherian ring, these are precisely the associated primes of a module . In that case the equivalent definition iswhere is a colon ideal. The decomposition terminology applies when a minimal primary decomposition exists; a general ring need not provide one for every ideal.