| http://www.w3.org/ns/prov#value | - In any particular model of $Z_2$, this function takes a formula of Peano arithmetic and returns T or F depending on whether that formula is true or false about the numbers in that model. $Z_2$ proves that every axiom of Peano arithmetic is sent to T by this function and that the truth value T is preserved by the inference rules of Peano arithmetic.
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