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