1. Splines (with optimal knots) are better;Burchard;Appl. Anal.,1974
2. Good approximation by splines with variable knots;de Boor,1973
3. Good approximation by splines with variables knots II;de Boor,1974
4. Optimal order approximation by polynomial spline functions. Technical Report;Dodson,1972
5. Convergence of segmented approximations of smooth functions on a bounded interval;McClure;Amer. Math. Soc. Notices,1970