Type II Unprojection
نویسنده
چکیده
Answering a question of M. Reid, we define and prove the Gorensteiness of the type II unprojection.
منابع مشابه
The equations of type II1 unprojection
The type II1 unprojection is, by definition, the generic complete intersection type II unprojection, in the sense of [P] Section 3.1, for the parameter value k = 1, and depends on a parameter n ≥ 2. Our main results are the explicit calculation of the linear relations of the type II1 unprojection for any value n ≥ 2 (Theorem 3.16) and the explicit calculation of the quadratic equation for the c...
متن کاملSome calculations on type II1 unprojection
The type II1 unprojection is, by definition, the generic complete intersection type II unprojection, in the sense of [P] Section 3.1, for the parameter value k = 1, and depends on a parameter n ≥ 2. Our main results are the explicit calculation of the linear relations of the type II1 unprojection for any value n ≥ 2 (Theorem 3.16) and the explicit calculation of the quadratic equation for the c...
متن کاملRemarks on Type III Unprojection
Type III unprojection plays a very important role in the birational geometry of Fano threefolds (cf. [CPR], [Ki], [BZ]). According to [Ki] p. 43, it was first introduced by A. Corti on his calculations of Fano threefolds of genus 6 and 7. It seems that at present a general definition of type III unprojection is still missing. After proving in Section 2 some general facts about residual ideals, ...
متن کاملParallel Kustin–miller Unprojection with an Application to Calabi–yau Geometry
Kustin–Miller unprojection constructs more complicated Gorenstein rings from simpler ones. Geometrically, it inverts certain projections, and appears in the constructions of explicit birational geometry. However, it is often desirable to perform not only one but a series of unprojections. The main aim of the present paper is to develop a theory, which we call parallel Kustin–Miller unprojection...
متن کاملKustin–Miller unprojection with complexes
A main ingredient for Kustin–Miller unprojection, as developed in [PR], is the module HomR(I, ωR), where R is a local Gorenstein ring and I a codimension one ideal with R/I Gorenstein. We prove a method of calculating it in a relative setting using resolutions. We give three applications. In the first we generalise a result of [CFHR]. The second and the third are about Tom and Jerry, two famili...
متن کامل