1. de Boor, C.: B-form basics. In: Geometric Modeling, 131?148. Farin, G. (ed.). SIAM, Philadelphia PA (1987)
2. de Boor, C., Höllig, K.: Approximation order from bivariateC 1-cubics: A counterexample. Proc. Am. Math. Soc.87, 649?655 (1983)
3. Farin, G.E.: Subsplines über Dreiecken. Diss. TU Braunschweig (1979)
4. Jia, R.-Q.: On the controlled approximation order from certain spaces of smooth bivariate splines. Math. Res. Center Tech. Summary Rep. # 2696 (1984)
5. Le Méhauté, Alain: On Hermite elements of classC q in ?3. In: Approximation Theory IV, 581?586. Chui, C., Schumaker, L.L., and Ward, J.D. (eds.) New York: Academic Press (1983)