# I Polynomials in n indeterminates and UFDs

1. Jun 11, 2016

### Math Amateur

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

2. Jun 11, 2016

### Staff: Mentor

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.

3. Jun 11, 2016

### Math Amateur

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

4. Jun 12, 2016

### Staff: Mentor

The induction step is: If a ring $R$ is UFD, so is $R[X]$.
(See http://math.harvard.edu/~waffle/ufds2.pdf [Broken]) 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).

Last edited by a moderator: May 8, 2017
5. Jun 12, 2016

### Math Amateur

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

Peter

Last edited by a moderator: May 8, 2017
6. Jun 13, 2016

### mathwonk

Last edited: Jun 13, 2016