L. Lusternik, Topology of functional spaces and calculus of variations in the large, Travaux Inst. Math. Stekloff, 19, 1947, 100 ñ. http://mi.mathnet.ru/book1045
Collected Works, Department of approximate calculations of the Mathematical Institute, USSR Academy of Sciences, Travaux Inst. Math. Stekloff, 20, ed. L. A. Lusternik, V. A. Ditkin, 1947, 136 ñ. http://mi.mathnet.ru/book1046
