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Studies in Rings generalised Unique Factorisation Rings

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Chapter 4<br />

INTRODUCTION<br />

LOCALISATION<br />

In this chapter, we <strong>in</strong>vestigate the localisation<br />

at prime ideals <strong>in</strong> GUFf{s. Persuaded by the importance<br />

of localisation <strong>in</strong> commutative r<strong>in</strong>gs and its application<br />

<strong>in</strong> t h c study of modules over c ommut a t i v e r<strong>in</strong>gs, several<br />

mathematicians <strong>in</strong>vestigated localisation at prime ideals<br />

<strong>in</strong> non-commutative r<strong>in</strong>gs, <strong>in</strong> particular <strong>in</strong> Noetherian<br />

r<strong>in</strong>gs, after Goldie proved his theorems for prime and<br />

semiprime Ncetherian r<strong>in</strong>gs.<br />

8 ut, bee()use 0 [ the 9 e nera 1 be la a v i 0 U r 0 f F) rime<br />

ideals <strong>in</strong> non-commutative r<strong>in</strong>gs, the complement of a<br />

prime ideal need not be a multiplicative set <strong>in</strong> general.<br />

Although the complement of every completely prime<br />

ideal<br />

<strong>in</strong> a Noetherian r<strong>in</strong>g is a multiplicative set, there are<br />

some completely prime ideals, whos e complements do<br />

not<br />

satisfy the ()re condition. Thus <strong>in</strong> general the<br />

localisation at the complement of a<br />

prime ideal can be<br />

ruled out <strong>in</strong> Noetherian r<strong>in</strong>gs.<br />

So,<br />

<strong>in</strong>stead of look<strong>in</strong>g at the complement of a<br />

prime ideal P <strong>in</strong> a<br />

Noetherian r<strong>in</strong>g R, jf we look at the<br />

set CR(P) = {r ~ R/r+P is regular <strong>in</strong> RIP} , then we<br />

can ga<strong>in</strong> someth<strong>in</strong>g. ~e say that a prime ideal <strong>in</strong> a

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