1. J. Bebernes -J. Schuur,Investigations in the topological method of Ważewski, Atti Accad. Naz. Lincei Rend. Cl. Sci. Fis. Mat. Natur.,49 (1970), pp. 39–42.
2. C. Berge,Espaces Topologiques. Functions Multivoques, Dunod, Paris (1966).
3. L. Jackson -G. Klaasen,A variation of Ważewski's topological method, SIAM J. Appl. Math.,20 (1971), pp. 124–130.
4. J.Kaplan - A.Lasota - J.Yorke,An application of the Ważewski retract method to boundary value problems, Zeszyty Nauk. Univ. Jagiellon. Prace Mat., to appear.
5. K. Kuratowski,Topology II, Academic Press, New York, 1968.