Samuel multiplicity for several commuting operators

Abstract

It is shown that the Samuel multiplicity of a lower semi-Fredholm tuple T\in L(X)^{n} of commuting bounded operators on a complex Banach space X coincides with the generic dimension of the last cohomolgoy groups H^{n}(z-T,X) of its Koszul complex near z=0. As applications we show that the algebraic and analytic Samuel multiplicities of T coincide and that the Samuel multiplicity is additive for closed invariant subspaces of the symmetric Fock space.