1. Integral Operators in the Theory of Linear Partial Differential Equations;Bergman,1969
2. Classes of solutions of linear partial differential equations in three variables;Bergman;Duke Math. J.,1946
3. Leçons sur les Propriétés Extrémales et la Meilleure Approximation des Fonctions Analytiques d'une Variable Réelle;Bernstein,1926
4. Function Theoretic Methods in Partial Differential Equations;Gilbert,1969
5. Constructive Methods of Elliptic Equations;Gilbert,1974