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 Pi(3)(1) set of integers: (iii) the set of stably categorical sentences using their revision operator V is similarly Pi(3)(1) and which is complete in Godel's universe of constructible sets L: (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.