Thom Isotopy Theorem for Nonproper Maps and Computation of Sets of Stratified Generalized Critical Values
AbstractLet $$X\subset {\mathbb {C}}^n$$ X ⊂ C n be an affine variety and $$f:X\rightarrow {\mathbb {C}}^m$$ f : X → C m be the restriction to X of a polynomial map $${\mathbb {C}}^n\rightarrow {\mathbb {C}}^m$$ C n → C m . We construct an affine Whitney stratification of X. The set K(f) of stratified generalized critical values of f can also be computed. We show that K(f) is a nowhere dense subset of $${\mathbb {C}}^m$$ C m which contains the set B(f) of bifurcation values of f by proving a version of the Thom isotopy lemma for nonproper polynomial maps on singular varieties.