1. Good approximation by splines with variable knots;de Boor, Carl,1973
2. Splines (with optimal knots) are better;Burchard, Hermann G.;Applicable Anal.,1973
3. T. Carleman, "Sur la résolution de certaines équations intégrales," Ark. Mat. Astronom. Fys., v. 16, 1921, pp. 1-19.
4. Monographies d'Informatique, No. 4;Cherruault, Y.,1968
5. D. S. Dodson, Optimal Order Approximation by Polynomial Spline Functions, Ph. D. Thesis, Comp. Sci. Dept., Purdue Univ., Lafayette, Ind., 1972.