On revision operators
PHILIP D. WELCH · Journal of Symbolic Logic · 2003
Abstract We look at various notions of a class of definability operations that generalise inductive operations, and are characterised as “revision operations”. More particularly we: (i) characterise therevision theoretically definablesubsets of a countable acceptable structure; (ii) show that the categorical truth set of Belnap and Gupta's theory of truth over arithmetic usingfullyvaried revision sequences yields a complete Σ31set of integers; (iii) the set ofstably categoricalsentences using their revision operator Ψ is similarly Σ31and which is complete in GÖdel's universe of constructive setsL; (iv) give an alternative account of a theory of truth—realistic variancethat simplifies full variance, whilst at the same time arriving at Kripkean fixed points.