Past exam of the mathematics course of the University of Cambridge 2026 iii Paper 101 5 a i Solution Created 2026-09-24 Updated 2026-09-25
For an -primary ideal in a Noetherian local ring, the functionagrees for all sufficiently large with a polynomial in . This is the Hilbert-Samuel polynomial, also called here the characteristic polynomial of . Using instead merely shifts its variable.
In the Noetherian local ring with maximal ideal , the embedding dimension is two but needs generators for every . The degree- monomials generate , and their images form a basis of , so no smaller generating list exists. These ideals are -primary: if and , then cannot be a unit; hence and . Consequently embedding dimension bounds the minimum over all maximal-primary ideals, because the maximal ideal itself is eligible, but does not bound the number of generators of each such ideal.
Prime-chain lower bound for local length 2026-10-06
A prime chain of length in a Noetherian local ring forces its maximal-ideal length function to be at least for large . Quotient by the initial prime to reduce to a domain, choose a nonzero in the next prime, and use the Artin-Rees lemma to obtain . Induction on chain length and summing about terms prove the bound. This yields without assuming the Krull height theorem.
System of parameters 2026-10-07
In a Noetherian local ring of dimension , a list whose generated ideal has radical . Such lists exist, by successively avoiding the finitely many top-dimensional minimal primes. No list shorter than can generate a maximal-primary ideal, by the Krull height theorem.