1. Helgason S., The Radon Transform, Birkhäuser, Basel (1980).
2. Courant R., Partial Differential Equations [Russian translation], Mir, Moscow (1964).
3. John F., Plane Waves and Spherical Means Applied to Partial Differential Equations, Springer-Verlag, Berlin, Heidelberg, and New York (1981).
4. Gel′fand I. M., Graev M. I., and Vilenkin N. Ya., Generalized Functions. Vol. 5: Integral Geometry and Representation Theory, Academic Press, New York and London (1966).
5. Lavrent′ev M. M. and Savel′ev L. Ya., Operator Theory and Ill-Posed Problems [in Russian], Sobolev Inst. Mat., Novosibirsk (1999).