Uniform boundedness principles for Sobolev maps into manifolds

Abstract

Given a connected Riemannian manifold N, an m-dimensional Riemannian manifold M which is either compact or the Euclidean space, p∈[1,+∞) and s∈(0,1], we establish, for the problems of surjectivity of the trace, of weak-bounded approximation, of lifting and of superposition, that qualitative properties satisfied by every map in a nonlinear Sobolev space Ws,p(M,N) imply corresponding uniform quantitative bounds. This result is a nonlinear counterpart of the classical Banach–Steinhaus uniform boundedness principle in linear Banach spaces.