Vassily M. Babich is a leading Russian expert in mathematical theory of diffraction and wave propagation. He is a co-author of ten monographs, and is the head of the laboratory of Mathematical Methods in Geophysics in the St. Petersburg branch of the Steklov Institute of Mathematics, as well as a part-time Professor at the Mathematical Faculty of St. Petersburg State University. Aleksei P. Kiselev has authored around 100 papers in diffraction and propagation of waves. He previously worked in seismic exploration, and in mechanical engineering at Leningrad (St. Petersburg). He is now a leading researcher in the Babich Laboratory, a part-time Professor at the Physical Faculty of St. Petersburg State University and a part-time researcher in the Institute of Mechanical Engineering.