1. V. N. Adrianov, Fundamentals of Radiative and Combined Heat Transfer [in Russian], Moscow (1972).
2. V. A. Ambartsumyan, Uchen, Zap. LGU, Ser. Matem.,37, 3 (1964).
3. V. I. Barkov, Zh. Vyshisl. Matem. i Matem. Fiz.,13, 1068 (1973).
4. G. Ya. Belov, Teplofiz. Vys. Temp.,10, 1268 (1972),
5. A. A. Gershun, Selected Works on Photometry and Illumination Engineering [in Russian], Moscow (1958).