  As indicated in our discussion, in Section 4, of the ‘iff’ in the T-biconditionals, Gupta and Belnap present the RTT as a special case of a revision theory of circularly defined concepts.  To reconsider the example from Section 4. Suppose that L is a language with a unary predicate F and a binary predicate R. Consider a new concept expressed by a predicate G, introduced through a definition, D, like this: 