1. The best approximation and differential properties of two conjugate functions;Bari;Trudy Moskov. Obšč.,1956
2. Interpolationsmethoden zur Behandlung von Approximationsprozessen auf Banachräumen;Berens,1968
3. The constructive theory of functions (1931–1953);Bernstein,1954
4. Semigroups of Operators and Approximation;Butzer,1967