Parameters and lim CM sequences: the Q-sequence conjecture and Lech's formula

Abstract

We prove that if a local ring has a weakly lim Cohen-Macaulay sequence of modules, then it satisfies the conjecture that every system of parameters is a Q-sequence. We also give a generalization of Lech's formula for the multiplicity of a local ring $(R,m)$ with respect to a system of parameters that allows a very large class of sequences of $m$-primary ideals generated by monomials in the parameters to be used in the calculation. The cases where the sequence of ideals consists of the powers of the ideal generated by parameters, or where the ideals in the sequence are generated by varying powers of the individual parameters all of which tend to infinity, which is Lech's original formula, are included.