  An algebraic version of Kashiwara and Schapira's calculus of constructible
functions is used to describe local topological properties of real algebraic
sets, including Akbulut and King's numerical conditions for a stratified set of
dimension three to be algebraic. These properties, which include
generalizations of the invariants modulo 4, 8, and 16 of Coste and Kurdyka, are
defined using the link operator on the ring of constructible functions.
