TY  - JOUR
AU  - Winfried Sickel
TI  - Necessary conditions on composition operators acting on Sobolev spaces of fractional order. The critical case 1 ... s ... n/p.
JO  - Forum mathematicum
PY  - 1997
SP  - 267
EP  - 302
VL  - 9
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/FORUM_1997__9_2_141803/
ID  - FORUM_1997__9_2_141803
ER  -