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Studies in Rings generalised Unique Factorisation Rings

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-35-<br />

Def<strong>in</strong>ition 2.2.<br />

An element a <strong>in</strong> a r<strong>in</strong>g R is said to be a normal<br />

element, if aR = Ra = 10<br />

In this case we call the<br />

ideal I, a<br />

normal, ideal.<br />

Def<strong>in</strong>ition 2 03.<br />

Let R be a Noetherian r<strong>in</strong>g with an over-r<strong>in</strong>g S.<br />

Then R is called a Generalised <strong>Unique</strong> factorisation r<strong>in</strong>g<br />

(GUFR), if every non-m<strong>in</strong>imal prime ideal of R conta<strong>in</strong>s<br />

a normal~S-<strong>in</strong>vertible ideal.<br />

Examples 2o~.<br />

(1) In any commutative Noetherian doma<strong>in</strong> 0 every<br />

nonzero prime ideal conta<strong>in</strong>s<br />

Q-<strong>in</strong>vertible pr<strong>in</strong>cipal<br />

ideals, where Q is the quotient field of D.<br />

Thus every<br />

commutative i'Joetherian <strong>in</strong>tegral doma<strong>in</strong> is a GUFR.<br />

(2) A Noetherian unique factorisation r<strong>in</strong>g, as def<strong>in</strong>ed<br />

<strong>in</strong> [2J is a prime Noetherian r<strong>in</strong>g R <strong>in</strong> which every non<br />

zero prime ideal conta<strong>in</strong>s a normal prime ideal. Tak<strong>in</strong>g<br />

S = Q(R), the simple Art<strong>in</strong>ian quotient r<strong>in</strong>g of R, it<br />

can be<br />

seen that every normal element <strong>in</strong> R is <strong>in</strong>vertible<br />

<strong>in</strong> S<br />

and thus every normal prime ideal is S-<strong>in</strong>vertible.<br />

So R is a<br />

prime GUFR.

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