Perfect ideal

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Short description: A type of ideal relevant for Noetherian rings

In commutative algebra, a perfect ideal is a proper ideal I in a Noetherian ring R such that its grade equals the projective dimension of the associated quotient ring.[1]

grade(I)=projdim(R/I).

A perfect ideal is unmixed.

For a regular local ring R a prime ideal I is perfect if and only if R/I is Cohen-Macaulay.

The notion of perfect ideal was introduced in 1913 by Francis Sowerby Macaulay[2] in connection to what nowadays is called a Cohen-Macaulay ring, but for which Macaulay did not have a name for yet. As Eisenbud and Gray[3] point out, Macaulay's original definition of perfect ideal I coincides with the modern definition when I is a homogeneous ideal in polynomial ring, but may differ otherwise. Macaulay used Hilbert functions to define his version of perfect ideals.

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