Truth as a predicate on the prosentential approach

According to the prosentential theory of truth, sentences that make use of "is true" as a predicate are to be paraphrased into sentences where "is true" occurs only in the form "that is true" or "it is true", which acts prosententially—i.e., related to a sentence in the way a pronoun is to a noun. Grover, Camp and Belnap in their account of the prosentential theory claim that the theory makes good on the idea that truth is not a predicate.

However, one can use a prosententially acceptable sentence to define what seems to be a perfectly fine truth predicate of sentences (either tokens or types, as one prefers—with Hartry Field, I prefer tokens) which I shall call "truth*":

s is true* if and only if there is a proposition such that s expresses (or, says) that it is true and it is true.

Here "it is true" is to be understood prosententially.