Basic classes for four-manifolds not of simple type

Abstract

We extend the notion of basic classes (for the Donaldson invariants) to 4-manifolds with b+ > 1 which are (potentially) not of simple type or satisfy b1 > 0.We also give a structure theorem for the Donaldson invariants of 4-manifolds with b+ > 1, b1 > 0 and of strong simple type.