1. N. E. Kochin, L. A. Kibel', and N. V. Roze, Theoretical Hydromechanics, Vol. 2 [in Russian], Fizmatgiz, Moscow (1963).
2. A. Friedman, Partial Differential Equations of Parabolic Type, Prentice-Hall (1964).
3. L. V. Ovsyannikov, ?General equations and examples,? collection: The Problem of Unseady Motion with a Free Boundary [in Russian], Nauka, Novosibirsk (1967), pp. 3?75.