1. I. G. Petrovskii, Lectures on Partial Differential Equations (Gostekhizdat, Moscow, 1950; Interscience Publ., New York, 1954).
2. T. A. Germogenova, Local Properties of Solutions to Transport Equation (Nauka, Moscow, 1986) [in Russian].
3. D. S. Anikonov, A. E. Kovtanyuk, and I.V. Prokhorov,Applications of Transport Equation to Tomography (Transport Equation and Tomography) (Logos, Moscow, 2000; VSP, Utrecht, 2002).
4. I. P. Natanson, Theory of Functions of a Real Variable (Nauka, Moscow, 1974; Ungar, New York, 1955 and 1961).
5. D. S. Konovalova, “Some Properties of Solutions to the Transport Equation,” Differetsial’nye Uravneniya 42(5), 684–689 (2006) [Differential Equations 42 (5), 732–738 (2006)].