Polynomials in n indeterminates and UFDs

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Discussion Overview

The discussion revolves around the unique factorization property of polynomial rings in multiple indeterminates over a field, specifically addressing the assertion made by Ernst Kunz in his book "Introduction to Plane Algebraic Curves." Participants are seeking proofs or references that substantiate this claim.

Discussion Character

  • Technical explanation
  • Exploratory
  • Homework-related

Main Points Raised

  • Peter requests a proof or reference for the statement that the polynomial ring ##K[X_1, X_2, \ldots, X_n]## is a unique factorization domain (UFD).
  • Some participants suggest demonstrating the property for one variable and using induction, noting that ##K[X_1, X_2, \ldots, X_n] = K[X_1, X_2, \ldots, X_{n-1}][X_n]##.
  • There is mention of applying the Euclidean algorithm in the case of one variable polynomials to find irreducible factors.
  • One participant expresses uncertainty about the setup and progression of the induction process.
  • Another participant provides a link to an article that outlines the induction step, stating that if a ring ##R## is a UFD, then ##R[X]## is also a UFD.
  • Additional resources are shared, including a graduate algebra book by Auslander and Buchsbaum, which discusses unique factorization domains.

Areas of Agreement / Disagreement

Participants generally agree on the approach of using induction to prove the unique factorization property, but there is no consensus on the specifics of the induction process or the completeness of the proof. Uncertainty remains regarding the details of the induction setup.

Contextual Notes

The discussion reflects a reliance on definitions and theorems related to unique factorization domains, with some participants pointing to external resources for further clarification. The completeness of the proof and the application of the induction principle are not fully resolved.

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In the introduction to Chapter 1 of his book "Introduction to Plane Algebraic Curves", Ernst Kunz states that the polynomial ring ##K[ X_1, X_2, \ ... \ ... \ , X_n]## over a field ##K## is a unique factorization domain ... ... but he does not prove this fact ...

Can someone demonstrate a proof of this proposition ... or point me to a text or online notes that contain a proof ...

Help will be appreciated ... ...

Peter
 
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You can show it for one variable and proceed by induction, because ##K[X_1,X_2, \dots , X_n] = K[X_1,X_2, \dots , X_{n-1}][X_n].##
For ##K[X]## you know that you can apply the Euclidean algorithm (division) to find all irreducible factors of a polynomial.
 
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fresh_42 said:
You can show it for one variable and proceed by induction, because ##K[X_1,X_2, \dots , X_n] = K[X_1,X_2, \dots , X_{n-1}][X_n].##
For ##K[X]## you know that you can apply the Euclidean algorithm (division) to find all irreducible factors of a polynomial.

Hmm ... yes, get the general idea ... but not quite sure how the induction is set up and how exactly it proceeds ... Thinking ...

Thanks for the help ...

Peter
 
Math Amateur said:
Hmm ... yes, get the general idea ... but not quite sure how the induction is set up and how exactly it proceeds ... Thinking ...

Thanks for the help ...

Peter
The induction step is: If a ring ##R## is UFD, so is ##R[X]##.
(See http://math.harvard.edu/~waffle/ufds2.pdf ) This brief article also contains a pretty good overview on some frequent classes of rings. I think you should read it to gain a feeling for the concepts and a pool of examples (14 pages).
 
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fresh_42 said:
The induction step is: If a ring ##R## is UFD, so is ##R[X]##.
(See http://math.harvard.edu/~waffle/ufds2.pdf ) This brief article also contains a pretty good overview on some frequent classes of rings. I think you should read it to gain a feeling for the concepts and a pool of examples (14 pages).

Thanks fresh_42 ... ... most helpful ... appreciate the help ...

Peter
 
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