DURFEE’S CONJECTURE ON THE SIGNATURE OF SMOOTHINGS OF SURFACE SINGULARITIES

Abstract

In 1978 Durfee conjectured various inequalities between the signature sigma and the geometric genus p(g) of a normal surface singularity. Since then a few counter examples have been found and positive results established in some special cases. We prove a ‘strong’ Durfee-type inequality for any smoothing of a Gorenstein singularity, provided that the intersection form of the resolution is unimodular. We also prove the conjectured ‘weak’ inequality for all hypersurface singularities and for sufficiently large multiplicity strict complete intersections. The proofs establish general inequalities valid for any numerically Gorenstein normal surface singularity.