CAT(0) is an algorithmic property

In this article we give an explicit algorithm which will determine, in a discrete and computable way, whether a finite piecewise Euclidean complex is nonpositively curved. In particular, given such a complex we show how to define a boolean combination of polynomial equations and inequalities in real variables, i.e. a real semi-algebraic set, which is empty if and only if the complex is nonpositively curved. Once this equivalence has been shown, the main result follows from a standard theorem in real algebraic geometry.