1. The Theory of Splines and Their Applications;Ahlberg,1967
2. Least squares cubic spline approximation, I. Fixed knots, II. Variable knots;de Boor;Purdue University Computer Science Dept. Tech. Reports 20 and 21,1968
3. On least squares approximation by spline functions;Houng,1973
4. On best L2 spline approximations;Powell;Intern. Ser. Num. Math.,1968
5. A generalized minimum norm property for spline functions with applications;Richards,1970