%0 Journal Article
%A Winfried Sickel
%T Necessary conditions on composition operators acting on Sobolev spaces of fractional order. The critical case 1 ... s ... n/p.
%J Forum mathematicum
%D 1997
%P 267-302
%V 9
%N 2
%I mathdoc
%U http://geodesic.mathdoc.fr/item/FORUM_1997__9_2_141803/
%F FORUM_1997__9_2_141803