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(* Title: ZF/Nat.thy
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ID: $Id$
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Author: Lawrence C Paulson, Cambridge University Computer Laboratory
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Copyright 1994 University of Cambridge
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Natural numbers in Zermelo-Fraenkel Set Theory
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*)
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Nat = OrdQuant + Bool + mono +
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consts
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nat :: i
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nat_case :: [i, i=>i, i]=>i
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nat_rec :: [i, i, [i,i]=>i]=>i
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defs
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nat_def "nat == lfp(Inf, %X. {0} Un {succ(i). i:X})"
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nat_case_def
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"nat_case(a,b,k) == THE y. k=0 & y=a | (EX x. k=succ(x) & y=b(x))"
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nat_rec_def
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"nat_rec(k,a,b) ==
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wfrec(Memrel(nat), k, %n f. nat_case(a, %m. b(m, f`m), n))"
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end
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