1. G. Asser, Das Reprä sentantenproblem im Prädikatenkalkül der ersten Stufe mit Identität, Z. Math. Logik Grundlag. Math. 1, 1955, pp. 252–263.
2. A. Durand, C. Lautemann and T. Schwentick, Subclasses of binary NP, Journal of Logic and Computation, to appear.
3. A. Durand and S. Ranaivoson, First-order spectra with one binary predicate, Theoretical Computer Science 160, 1–2, 1996, pp. 305–320.
4. S. Eilenberg, Automata, Languages, and Machines, Vol. A, Academic Press, New York and London, 1974.
5. H. Enderton, A Mathematical Introduction to Logic, Academic Press, New York and London, 1972.