1. Ackermann, W.: 1962, Solvable Cases of the Decision Problem, North-Holland, Amsterdam.
2. Altham, J. E. J. and Tennant, N. W.: 1975, ‘Sortal quantification’, in E. L. Keenan [1975] pp. 46–58.
3. Anderson, J. M. and Johnstone Jr., H. W.: 1962, Natural Deduction: the Logical Basis of Axiom Systems, Wadsworth, Belmont, California.
4. Ax, J. and Kochen, S.: 1965, ‘Diophantine problems over local fields: I’, Amer. J. Math. 87, 605–630.
5. Bar-Hillel, Y.: 1971, Pragmatics of Natural Languages, Reidel, Dordrecht.