In 1953 LeVeque proved the existence of \(U_m\) -numbers by showing that for some specially defined Liouville number \(\lambda \) , the mth root \(\lambda ^{1/m}\) is in \(U_m\) . In this article we study the following question: let u be an algebraic function of degree m and \(\lambda \) a Liouville number; under which conditions is \(u(\lambda )\) a \(U_m\) -number? We consider a more refined notion of \(\mathcal {L}\) -numbers, and show that, under very general assumptions, an algebraic function of degree m takes \(U_m\) -values at all \(\mathcal {L}\) -numbers.