1) The Nullstellensatz and the R-Nullstellensatz. 2) Chevalley’s Theorem: the image of a constructible set is constructible. 3) (Grothendieck, Ax) An injective polynomial map from C to C is surjective. 4) Hilbert’s 17th problem: a positive semidefinite rational function f ∈ R(t1, . . . , tn) is a sum of squares. 5) Polynomially compact operators have invariant subspaces. (Let V be a complex Hil...