Monthly Archives: April 2020

Commutative Algebra 42

Noether Normalization Theorem Throughout this article, k is a field, not necessarily algebraically closed. Definition. Let A be a finitely generated k-algebra which is an integral domain. We say are algebraically independent over k if they are so as elements … Continue reading

Posted in Advanced Algebra | Tagged , , , , , | 4 Comments

Commutative Algebra 41

Basic Definitions The objective of this article is to establish the theory of transcendence bases for field extensions. Readers who are already familiar with this may skip the article. We will focus on field extensions here. Definition. Let be a … Continue reading

Posted in Advanced Algebra | Tagged , , , | 2 Comments

Commutative Algebra 40

More on Integrality Lemma 1. Let be an integral extension. If is an ideal and , the resulting injection is an integral extension. Proof Any element of can be written as , . Then x satisfies a monic polynomial relation: . … Continue reading

Posted in Advanced Algebra | Tagged , , , , , , | 4 Comments

Commutative Algebra 39

Integrality Throughout this article, A is a subring of B; we will also call B a ring extension of A. Definition. An element is said to be integral over A if we can find (where ) such that in B. For example, is integral over since … Continue reading

Posted in Advanced Algebra | Tagged , , , , , , | Leave a comment

Commutative Algebra 38

Artinian Rings The main result we wish to prove is the following. Theorem. A ring A is artinian if and only if it is noetherian and , where denotes the Krull dimension. Note Recall that means all prime ideals of A … Continue reading

Posted in Advanced Algebra | Tagged , , , | Leave a comment

Commutative Algebra 37

Artinian Modules Instead of the ascending chain condition, we can take its reverse. Definition. Let M be an A-module. Consider the set of submodules of M, ordered by inclusion, i.e. if and only if . We say M is artinian … Continue reading

Posted in Advanced Algebra | Tagged , , , , , | Leave a comment

Commutative Algebra 36

In this article, we will study the topology of Spec A when A is noetherian. For starters, let us consider irreducible topological spaces in greater detail. Irreducible Spaces Recall that an irreducible topological space is a non-empty space X satisfying any of the … Continue reading

Posted in Advanced Algebra | Tagged , , , , | Leave a comment