1. [1] P. Appell and J. Kampé de Fériet. Fonctions Hypergéometriques et Hypersphériques, Polynome d'Hermite. Gauthier-Villars, Paris, 1926.
2. [2] G. Darboux. Théorie Générale des Surfaces. Gauthier-Villars, Paris, 1888-96.
3. [3] V. Kh. Froim. Linear scalar partial differential equations with regular singularities on a hypersurface. Differencial’nye Uravneniya 9 (1973), 533-541.
4. [4] V. Kh. Froim. The representation of analytic solutions of certain partial differential equations with coefficients having pole-type singularities with respect to one argument. Differencial’nye Uravneniya 7 (1951), 142-156.
5. [5] V. Kh. Froim. Linear partial differential equations whose coefficients have pole type singularities in one argument only. Siberian Math. J. 11 (1970), 625-647.