[5] O. Vejvoda:
Periodic solutions of nonlinear partial differential equations of evolution. Equadiff II, Differential Equations and their Applications, Proceedings of the Conference, Bratislava 1966, published in Acta Facultatis Rerum Naturalium Universitatis Comenianae, Mathetica, 77 (1967), 293-300.
MR 0249793