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Studies in Rings generalised Unique Factorisation Rings

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-1 lC)-<br />

Def<strong>in</strong>i.tion 4 038.<br />

Let R be a Noetherian r<strong>in</strong>g. A subset X of Spec R<br />

is said to be a .§J2arse<br />

subset if, given any Q € .Spec R<br />

and given any c £ CR(Q), we have<br />

Remark 4 039.<br />

Let R be a GUFR and I be a normal <strong>in</strong>vertible<br />

ideal of R. Put X I<br />

= '.p, Spec RI height P = 1 and I < pJ<br />

Then by pr<strong>in</strong>cipal ideal theorem XI /: (fjo LetQ ~ Spec 11<br />

and c £ C(Q). Then, if Q is m<strong>in</strong>imal,! cannot be<br />

conta<strong>in</strong>ed <strong>in</strong> Q, s<strong>in</strong>ce R is a GUFR, whereas<br />

n{p ~ XII Q < P and C f- C R<br />

(P)J conta<strong>in</strong>s I. Further,<br />

if Q is nonm<strong>in</strong>imal, then height of Q ~ 1 and so there<br />

exists no height 1 prime P such that Q < P and so<br />

'..{p E XI/Q < P, c ~ CR(P~== \21. Thus <strong>in</strong> both cases<br />

o f:: n{p f xr/o< P, c f- CR(P)J. Therefore X r is a<br />

s pa r s e set <strong>in</strong> R.<br />

The 0 r ern 4 0 40 •<br />

Let R be a GUFR and I be a normal <strong>in</strong>vertible ideal<br />

of R. Also assume that for a prime idealQ,{PE. XI/Q ~pJ<br />

is right s t ab Le , Then [p E. Xr/O ~pJ is a c La s s i c a l Ly<br />

right localis~ble<br />

seto

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