Introduction

Abstract

Classical Intersection Theory (see for example Weil [Wei]) treats the case of proper intersections, where geometrical objects (usually subvarieties of a nonsingular variety) intersect with the expected dimension. In 1984, two books appeared which surveyed and developed work by the individual authors, coworkers and others on a refined version of Intersection Theory, treating the case of possibly improper intersections, where the intersection could have excess dimension. The first, by W. Fulton [Ful1] (recently revised in updated form), used a geometrical theory of deformation to the normal cone, more specifically, deformation to the normal bundle followed by moving the zero section to make the intersection proper; this theory was due to the author together with R. MacPherson and worked generally for intersections on algebraic manifolds. It represents nowadays the standard approach to Intersection Theory.