1. Brosowski, B.: Nicht-lineare Tschebyscheff-Approximation. B. I. Mannheim 1968.
2. Burov, V. N.: The approximation of functions by polynomials satisfying nonlinear relations. Dokl. Akad. Nauk. SSSR138, 515–517 (1961).
3. Cheney, E. W.: Introduction to approximation theory. New York-St. Louis: McGraw-Hill 1966.
4. Deutsch, F.: On uniform approximation with interpolatory constraints. SIAM J. Appl. Math.24, 62–79 (1968).
5. Duffin, R. R., Karlovitz, L. A.: Formulation of linear programs in analysis I: Approximation theory. SIAM J. Appl. Math.16, 662–675 (1968).