On revision operators

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 the revision theoretically definable subsets of a countable acceptable structure; (ii) show that the categorical truth set of Belnap and Gupta’s theory of truth over arithmetic using fully varied revision sequences yields a complete set of integers; (iii) the set of stably categorical sentences using their revision operator is similarly and which is complete in Gödel’s universe of constructible sets ; (iv) give an alternative account of a theory of truth realistic variance that simplifies full variance, whilst at the same time arriving at Kripkean fixed points. [...] no statement is immune to revision. W. V. O. Quine, From a Logical Point of View, p 43.