Generalised Hilbert Numerators II

Abstract

We associate to each $r$-multigraded, locally finitely generated ideal in the "large polynomial ring" on countably many indeterminates a power series in $r$ variables; this power series is the limit in the adic topology of the numerators of the rational functions which give the Hilbert series of the truncations of the ideal. We characterise the set of all power series so obtained. Our main technical tools are an approximation result which asserts that truncation and the forming of initial ideals commute in a filtered sense, and standard inclusion/exclusion, Möbius inversion, and LCM-lattice homology methods generalised to monomial ideals in countably many variables.