"Resolving social conflicts; selected papers on group dynamics" edited by Gertrude W. Lewin New York: Harper & Row, 1948, p. 133; as cited in "Schooling & Capitalism: A Sociological Reader" by Roger Dale, Madeleine MacDonald, Geoff Esland, (p. 111), 1976.
Max Beckmann, Barbara Copeland Buenger (1997). “Self-Portrait in Words: Collected Writings and Statements, 1903-1950”, p.307, University of Chicago Press