1. S. Bloom andR. Suszko,Investigations into the Sentential Calculus with Identity, (to apper in the Notre Dame Journal of Formal Logic).
2. G. Gratzer,Universal Algebra, Van Nostrand 1968.
3. C. I. Lewis, C. H. Langford,Symbolic Logic, New York (1962).
4. J. C. McKinsey, A. Tarski, J. Symbolic Logic 13, (1948) 1–15.
5. R. Suszko,Ontology in the Tractatus of Wittgenstein, Notre Dame Journal of Formal Logic, 9 (1968) 7–33.