Rationality of semialgebraic functions

Abstract

Let X be an algebraic subset of Rⁿ, and ƒ: X → R a semialgebraic function. We prove that if ƒ is continuous rational on each curve C ⊂ X then: 1) ƒ is arc-analytic, 2) ƒ is continuous rational on X. As a consequence we obtain a characterization of hereditarily rational functions recently studied by J. Kollár and K. Nowak.