(* Title: ZF/bool.thy
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1992 University of Cambridge
Booleans in Zermelo-Fraenkel Set Theory
*)
Bool = ZF +
consts
"1" :: "i" ("1")
bool :: "i"
cond :: "[i,i,i]=>i"
not :: "i=>i"
and :: "[i,i]=>i" (infixl 70)
or :: "[i,i]=>i" (infixl 65)
xor :: "[i,i]=>i" (infixl 65)
rules
one_def "1 == succ(0)"
bool_def "bool == {0,1}"
cond_def "cond(b,c,d) == if(b=1,c,d)"
not_def "not(b) == cond(b,0,1)"
and_def "a and b == cond(a,b,0)"
or_def "a or b == cond(a,1,b)"
xor_def "a xor b == cond(a,not(b),b)"
end