Towards Proof-Theoretic Formulation of the General Theory of Term-Forming Operators

Abstract Term-forming operators (tfos), like iota- or epsilon-operator, are technical devices applied to build complex terms in formal languages. Although they very useful practice their theory is not well developed. In the paper we provide a proof-theoretic formulation of general approach tfos provided independently by several authors Scott, Hatcher, Corcoran, and compare it with an proposed later Tennant. Eventually shown how can be specific areas Quine’s set NF.