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(* Title: ZF/Bool.thy
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1992 University of Cambridge
*)
section\<open>Booleans in Zermelo-Fraenkel Set Theory\<close>
theory Bool imports pair begin
abbreviation
one (\<open>1\<close>) where
"1 == succ(0)"
abbreviation
two (\<open>2\<close>) where
"2 == succ(1)"
text\<open>2 is equal to bool, but is used as a number rather than a type.\<close>
definition "bool == {0,1}"
definition "cond(b,c,d) == if(b=1,c,d)"
definition "not(b) == cond(b,0,1)"
definition
"and" :: "[i,i]=>i" (infixl \<open>and\<close> 70) where
"a and b == cond(a,b,0)"
definition
or :: "[i,i]=>i" (infixl \<open>or\<close> 65) where
"a or b == cond(a,1,b)"
definition
xor :: "[i,i]=>i" (infixl \<open>xor\<close> 65) where
"a xor b == cond(a,not(b),b)"
lemmas bool_defs = bool_def cond_def
lemma singleton_0: "{0} = 1"
by (simp add: succ_def)
(* Introduction rules *)
lemma bool_1I [simp,TC]: "1 \<in> bool"
by (simp add: bool_defs )
lemma bool_0I [simp,TC]: "0 \<in> bool"
by (simp add: bool_defs)
lemma one_not_0: "1\<noteq>0"
by (simp add: bool_defs )
(** 1=0 ==> R **)
lemmas one_neq_0 = one_not_0 [THEN notE]
lemma boolE:
"[| c: bool; c=1 ==> P; c=0 ==> P |] ==> P"
by (simp add: bool_defs, blast)
(** cond **)
(*1 means true*)
lemma cond_1 [simp]: "cond(1,c,d) = c"
by (simp add: bool_defs )
(*0 means false*)
lemma cond_0 [simp]: "cond(0,c,d) = d"
by (simp add: bool_defs )
lemma cond_type [TC]: "[| b: bool; c: A(1); d: A(0) |] ==> cond(b,c,d): A(b)"
by (simp add: bool_defs, blast)
(*For Simp_tac and Blast_tac*)
lemma cond_simple_type: "[| b: bool; c: A; d: A |] ==> cond(b,c,d): A"
by (simp add: bool_defs )
lemma def_cond_1: "[| !!b. j(b)==cond(b,c,d) |] ==> j(1) = c"
by simp
lemma def_cond_0: "[| !!b. j(b)==cond(b,c,d) |] ==> j(0) = d"
by simp
lemmas not_1 = not_def [THEN def_cond_1, simp]
lemmas not_0 = not_def [THEN def_cond_0, simp]
lemmas and_1 = and_def [THEN def_cond_1, simp]
lemmas and_0 = and_def [THEN def_cond_0, simp]
lemmas or_1 = or_def [THEN def_cond_1, simp]
lemmas or_0 = or_def [THEN def_cond_0, simp]
lemmas xor_1 = xor_def [THEN def_cond_1, simp]
lemmas xor_0 = xor_def [THEN def_cond_0, simp]
lemma not_type [TC]: "a:bool ==> not(a) \<in> bool"
by (simp add: not_def)
lemma and_type [TC]: "[| a:bool; b:bool |] ==> a and b \<in> bool"
by (simp add: and_def)
lemma or_type [TC]: "[| a:bool; b:bool |] ==> a or b \<in> bool"
by (simp add: or_def)
lemma xor_type [TC]: "[| a:bool; b:bool |] ==> a xor b \<in> bool"
by (simp add: xor_def)
lemmas bool_typechecks = bool_1I bool_0I cond_type not_type and_type
or_type xor_type
subsection\<open>Laws About 'not'\<close>
lemma not_not [simp]: "a:bool ==> not(not(a)) = a"
by (elim boolE, auto)
lemma not_and [simp]: "a:bool ==> not(a and b) = not(a) or not(b)"
by (elim boolE, auto)
lemma not_or [simp]: "a:bool ==> not(a or b) = not(a) and not(b)"
by (elim boolE, auto)
subsection\<open>Laws About 'and'\<close>
lemma and_absorb [simp]: "a: bool ==> a and a = a"
by (elim boolE, auto)
lemma and_commute: "[| a: bool; b:bool |] ==> a and b = b and a"
by (elim boolE, auto)
lemma and_assoc: "a: bool ==> (a and b) and c = a and (b and c)"
by (elim boolE, auto)
lemma and_or_distrib: "[| a: bool; b:bool; c:bool |] ==>
(a or b) and c = (a and c) or (b and c)"
by (elim boolE, auto)
subsection\<open>Laws About 'or'\<close>
lemma or_absorb [simp]: "a: bool ==> a or a = a"
by (elim boolE, auto)
lemma or_commute: "[| a: bool; b:bool |] ==> a or b = b or a"
by (elim boolE, auto)
lemma or_assoc: "a: bool ==> (a or b) or c = a or (b or c)"
by (elim boolE, auto)
lemma or_and_distrib: "[| a: bool; b: bool; c: bool |] ==>
(a and b) or c = (a or c) and (b or c)"
by (elim boolE, auto)
definition
bool_of_o :: "o=>i" where
"bool_of_o(P) == (if P then 1 else 0)"
lemma [simp]: "bool_of_o(True) = 1"
by (simp add: bool_of_o_def)
lemma [simp]: "bool_of_o(False) = 0"
by (simp add: bool_of_o_def)
lemma [simp,TC]: "bool_of_o(P) \<in> bool"
by (simp add: bool_of_o_def)
lemma [simp]: "(bool_of_o(P) = 1) \<longleftrightarrow> P"
by (simp add: bool_of_o_def)
lemma [simp]: "(bool_of_o(P) = 0) \<longleftrightarrow> ~P"
by (simp add: bool_of_o_def)
end