@article {191,
	title = {Normals of subdivision surfaces and their control polyhedra},
	journal = {Computer Aided Geometric Design},
	volume = {24},
	year = {2007},
	pages = {112-116},
	author = {Ingo Ginkel and J{\"o}rg Peters and Georg Umlauf}
}
@conference {215,
	title = {On normals and control nets},
	booktitle = {Mathematics of Surfaces XI},
	year = {2005},
	publisher = {Springer-Verlag},
	organization = {Springer-Verlag},
	author = {Ingo Ginkel and J{\"o}rg Peters and Georg Umlauf},
	editor = {R.~Martin and H.~Bez and M.~Sabin pages = 233-239}
}
