Singular implicit and inverse function theorems. Strong resolution with normally flat centers

TL;DR

This paper generalizes the inverse and implicit function theorems to handle singularities defined by ideals of higher multiplicity, providing new tools for desingularization and a canonical approach in characteristic zero.

Contribution

It introduces a singular inverse and implicit function theorem for larger multiplicity ideals, extending classical results and applications to desingularization.

Findings

Extended inverse and implicit function theorems for singularities

Application to desingularization and Hironaka normal flatness

Canonical Rees algebra along Samuel stratum in characteristic zero

Abstract

Building upon ideas of Hironaka, Bierstone-Milman, Malgrange and others we generalize the inverse and implicit function theorem (in differential, analytic and algebraic setting) to sets of functions of larger multiplicities (or ideals). This allows one to describe singularities given by a finite set of generators or by ideals in a simpler form. In the special Cohen-Macaulay case we obtain a singular analog of the inverse function theorem. The singular implicit function theorem is closely related to a (proven here) extended version of the Weierstrass-Hironaka-Malgrange division and preparation theorems. The primary motivation for this paper comes from the desingularization problem. As an illustration of the techniques used, we give some applications of our theorems to desingularization extending some results on Hironaka normal flatness, the Samuel stratification and the Hilbert-Samuel function. The notion of the standard basis along Samuel stratum introduced in the paper (inspired by the Bierstone-Milman and Hironaka constructions) allows us to describe singularities along the Samuel stratum in a relatively simple way. It leads to a canonical reduction of the strong Hironaka desingularization with normally flat centers to a so called resolution of marked ideals. Moreover, in characteristic zero, the standard basis along Samuel stratum generates a unique canonical Rees algebra along Samuel startum giving a straightforward proof of the strong desingularization in algebraic and analytic cases.