Hi Tyglik,

Thanks for correcting my errors. Guess I need to do my homework more properly ;-)

Anyway, for those interested in the topic of the convergence of NURBS and SDS the article on extended subdivision surfaces is higly recommended. It seems like ESUBS offer even more possibilities than T-NURCC surfaces (t-splines).
Here is the link:

http://portal.acm.org/citation.cfm?id=1138455

Happy modeling!!!