1. On the Riemann-Green function;Copson;Archive for Rational Mechanics and Analysis,1958
2. On the use of infinitesimal transformations to find the Riemann (-Green) function;Daggit,1968
3. Partial Differential Equations;Garabedian,1964
4. Über die Integration durch bestimmte Integrale von einer Klasse linearer partieller Differentialgleichungen;Sophus,1922