This module extends the HOL logic with the theory of natural numbers. This involves giving theory object definitions for the naturals base type and the "ZERO" and "SUC" constants, based on the theory of individuals, and proving a few important properties.
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"IsNatRep" is the characteristic function for the naturals base type, prescribing the subset of `:ind` used to represent naturals. It is defined as the function that returns `true` for a given `:ind` element iff any property that holds for "IND_ZERO" and all its successors under "IND_SUC" necessarily holds for the element. This gives the smallest subset of `:ind` containing "IND_ZERO" and closed under "IND_SUC". |- !i. IsNatRep i <=> (!P. P IND_ZERO /\ (!j. P j ==> P (IND_SUC j)) ==> P i)
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