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- Jun 22, 2012

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**Proposition 10: In an integral domain a prime element is always irreducible.**

The proof reads as follows:

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Suppose (p) is a non-zero prime ideal and p = ab.

Then [TEX] ab = p \in (p) [/TEX], so by definition of prime ideal, one of a or b, say a, is in (p).

Thus a = pr for some r.

This implies p = ab = prb and so rb = 1 and b is a unit.

This shows that p is irreducible.

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My question is as follows: Where in this proof do D&F use the fact that p is in an integral domain??? (It almost reads as if this applies for any ring)

Peter