David J. Lieberman (2010). “Find Out Who's Normal and Who's Not: The Proven System to Quickly Assess Anyone's Emotional Stability”, p.161, David Lieberman
"International Systems: Peace, Conflict Resolution, and Politics" (1975) by Kenneth Boulding (p. 375), as quoted in "Non-offensive defence for the twenty-first century" by Bjørn Møller, Håkan Wiberg, (p. 36), 1994.