1. S. Alexander, Space, Time and Deity (Macmillan, London, 1920), Vol. 2, p. 46.
2. Hempel, Aspects of Scientific Explanation (Free Press, New York, 1965), pp. 259 ff.
3. E. Nagel, The Structure of Science (Routledge, London, 1961), p. 364.
4. K. Popper, Objective Knowledge (Oxford University Press, Oxford, 1972), p. 290.
5. E. Schrödinger, What is Life? (Cambridge University Press, Cambridge, 1945), p. 2.