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Hilbert–Burch theorem

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Describes the structure of some free resolutions of a quotient of a local or graded ring

In mathematics, the Hilbert–Burch theorem describes the structure of some free resolutions of a quotient of a local or graded ring in the case that the quotient has projective dimension 2. Hilbert (1890) proved a version of this theorem for polynomial rings, and Burch (1968, p. 944) proved a more general version. Several other authors later rediscovered and published variations of this theorem. Eisenbud (1995, theorem 20.15) gives a statement and proof.

Statement

If R is a local ring with an ideal I and

0 R m f R n R R / I 0 {\displaystyle 0\rightarrow R^{m}{\stackrel {f}{\rightarrow }}R^{n}\rightarrow R\rightarrow R/I\rightarrow 0}

is a free resolution of the R-module R/I, then m = n – 1 and the ideal I is aJ where a is a regular element of R and J, a depth-2 ideal, is the first Fitting ideal Fitt 1 I {\displaystyle \operatorname {Fitt} _{1}I} of I, i.e., the ideal generated by the determinants of the minors of size m of the matrix of f.

References


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