Theory of sets 论文

摘要

The theory of sets is a theory which contains the relational signs =, ∈ and the substantific sign ⊃ (all these signs being of weight 2); in addition to the schemes S1 to S7 given in Chapter I, it contains the scheme S8, which will be introduced in no. 6, and the explicit axioms Al (no. 3.) A2 (no. 5), A3 (§ 2, no. 1), A4 (§ 5, no. 1), and A5 (Chapter III, § 6, no. 1), These explicit axioms contain no letters; in other words, the theory of sets is a theory without constants.