is a homeomorphism, then the
inverse mapping is in the 
class and the formula on differentiation of
can be derived. For Sobolev regularity of the inverse mapping the
assumption of finite distortion is relevant. Based on joint results with
Katarína Bellová, Marianna Csörnyei, Stanislav Hencl, Pekka Koskela
and Jani Onninen.