On positively differentiable curves with values in normed linear spaces

We prove a theorem that characterizes continuous normed linear space-valued curves allowing differentiable parameterizations with non-zero derivatives as those curves, all the points of which are regular (in Choquet’s sense). We also state an equivalent geometric condition not involving any homeomorphisms. This extends a theorem due to Choquet, who proved a similar result for curves with values in Euclidean spaces. © 2005 Elsevier Inc. All rights reserved