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Normal Transversality and Uniform Bounds
Authors:Planas-Vilanova  Francesc
Institution:Departament de Matemàtica Aplicada 1, ETSEIB, Universitat Politècnica de Catalunya Diagonal 647, E-08028 Barcelona, Spain, planas{at}ma1.upc.es
Abstract:Let A be a commutative ring. A graded A-algebra U = {oplus}n≥0 Un isa standard A-algebra if U0 = A and U = AU1] is generated asan A-algebra by the elements of U1. A graded U-module F = {oplus}n≥0Fnis a standard U-module if F is generated as a U-module by theelements of F0, that is, Fn = UnF0 for all n ≥ 0. In particular,Fn = U1Fn–1 for all n ≥ 1. Given I, J, two ideals of A,we consider the following standard algebras: the Rees algebraof I, R(I) = {oplus}n≥0Intn = AIt] sub At], and the multi-Rees algebraof I and J, R(I, J) = {oplus}n≥0({oplus}p+q=nIpJqupvq) = AIu, Jv] sub Au, v].Consider the associated graded ring of I, G(I) = R(I) {otimes} A/I ={oplus}n≥0In/In+1, and the multi-associated graded ring of I and J,G(I, J) = R(I, J) {otimes} A/(I+J) = {oplus}n≥0({oplus}p+q=nIpJq/(I+J)IpJq). We canalways consider the tensor product of two standard A-algebrasU = {oplus}p≥0Up and V = {oplus}q≥0Vq as a standard A-algebra with the naturalgrading U {otimes} V = {oplus}n≥0({oplus}p+q=nUp {otimes} Vq). If M is an A-module, we havethe standard modules: the Rees module of I with respect to M,R(I; M) = {oplus}n≥0InMtn = MIt] sub Mt] (a standard R(I)-module), andthe multi-Rees module of I and J with respect to M, R(I, J;M) = {oplus}n≥0({oplus}p+q=nIpJqMupvq) = MIu, Jv] sub Mu, v] (a standard R(I,J)-module). Consider the associated graded module of M withrespect to I, G(I; M) = R(I; M) {otimes} A/I = {oplus}n≥0InM/In+1M (a standardG(I)-module), and the multi-associated graded module of M withrespect to I and J, G(I, J; M) = R(I, J; M) {otimes} A/(I+J) = {oplus}n≥0({oplus}p+q=nIpJqM/(I+J)IpJqM)(a standard G(I, J)-module). If U, V are two standard A-algebras,F is a standard U-module and G is a standard V-module, thenF {otimes} G = {oplus}n≥0({oplus}p+q=nFp {otimes} Gq) is a standard U {otimes} V-module. Denote by {pi}:R(I) {otimes} R(J; M) -> R(I, J; M) and {sigma}:R(I, J; M) -> R(I+J;M) the natural surjective graded morphisms of standard RI) {otimes}R(J)-modules. Let {varphi}:R(I) {otimes} R(J; M) -> R(I+J; M) be {sigma}{circ}{pi}. Denote by Formula:G(I) {otimes} G(J; M) -> G(I, J; M) and Formula:G(I, J; M) -> G(I+J; M) the tensor productof {pi} and {sigma} by A/(I+J); these are two natural surjective gradedmorphisms of standard G(I) {otimes} G(J)-modules. Let Formula:G(I) {otimes} G(J; M) -> G(I+J; M) be Formula{circ}Formula. The first purpose of this paper is to prove the following theorem.
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