@inproceedings{Prautzsch1992Simple,
  Author = {Hartmut Prautzsch and Wilfried Trump},
  Title = {Simple surfaces have no simple C<sup>1</sup> parametrization},
  Booktitle = {},
  Year = {1992},
  Note = {In: T. Lyche, L.L. Schumaker (eds.), Mathematical Methods in CAGD II, Academic Press, 1992: 475-480}
}