src/CCL/Hered.thy
 author wenzelm Mon, 16 Jun 2008 22:13:39 +0200 changeset 27239 f2f42f9fa09d parent 27208 5fe899199f85 child 28262 aa7ca36d67fd permissions -rw-r--r--
pervasive RuleInsts;
```
(*  Title:      CCL/Hered.thy
ID:         \$Id\$
Author:     Martin Coen
*)

header {* Hereditary Termination -- cf. Martin Lo\"f *}

theory Hered
imports Type
begin

text {*
Note that this is based on an untyped equality and so @{text "lam
x. b(x)"} is only hereditarily terminating if @{text "ALL x. b(x)"}
is.  Not so useful for functions!
*}

consts
(*** Predicates ***)
HTTgen     ::       "i set => i set"
HTT        ::       "i set"

axioms
(*** Definitions of Hereditary Termination ***)

HTTgen_def:
"HTTgen(R) == {t. t=true | t=false | (EX a b. t=<a,b>      & a : R & b : R) |
(EX f.  t=lam x. f(x) & (ALL x. f(x) : R))}"
HTT_def:       "HTT == gfp(HTTgen)"

subsection {* Hereditary Termination *}

lemma HTTgen_mono: "mono(%X. HTTgen(X))"
apply (unfold HTTgen_def)
apply (rule monoI)
apply blast
done

lemma HTTgenXH:
"t : HTTgen(A) <-> t=true | t=false | (EX a b. t=<a,b> & a : A & b : A) |
(EX f. t=lam x. f(x) & (ALL x. f(x) : A))"
apply (unfold HTTgen_def)
apply blast
done

lemma HTTXH:
"t : HTT <-> t=true | t=false | (EX a b. t=<a,b> & a : HTT & b : HTT) |
(EX f. t=lam x. f(x) & (ALL x. f(x) : HTT))"
apply (rule HTTgen_mono [THEN HTT_def [THEN def_gfp_Tarski], THEN XHlemma1, unfolded HTTgen_def])
apply blast
done

subsection {* Introduction Rules for HTT *}

lemma HTT_bot: "~ bot : HTT"
by (blast dest: HTTXH [THEN iffD1])

lemma HTT_true: "true : HTT"
by (blast intro: HTTXH [THEN iffD2])

lemma HTT_false: "false : HTT"
by (blast intro: HTTXH [THEN iffD2])

lemma HTT_pair: "<a,b> : HTT <->  a : HTT  & b : HTT"
apply (rule HTTXH [THEN iff_trans])
apply blast
done

lemma HTT_lam: "lam x. f(x) : HTT <-> (ALL x. f(x) : HTT)"
apply (rule HTTXH [THEN iff_trans])
apply auto
done

lemmas HTT_rews1 = HTT_bot HTT_true HTT_false HTT_pair HTT_lam

lemma HTT_rews2:
"one : HTT"
"inl(a) : HTT <-> a : HTT"
"inr(b) : HTT <-> b : HTT"
"zero : HTT"
"succ(n) : HTT <-> n : HTT"
"[] : HTT"
"x\$xs : HTT <-> x : HTT & xs : HTT"

lemmas HTT_rews = HTT_rews1 HTT_rews2

subsection {* Coinduction for HTT *}

lemma HTT_coinduct: "[|  t : R;  R <= HTTgen(R) |] ==> t : HTT"
apply (erule HTT_def [THEN def_coinduct])
apply assumption
done

ML {*
fun HTT_coinduct_tac ctxt s i = res_inst_tac ctxt [(("R", 0), s)] @{thm HTT_coinduct} i
*}

lemma HTT_coinduct3:
"[|  t : R;   R <= HTTgen(lfp(%x. HTTgen(x) Un R Un HTT)) |] ==> t : HTT"
apply (erule HTTgen_mono [THEN [3] HTT_def [THEN def_coinduct3]])
apply assumption
done

ML {*
val HTT_coinduct3_raw = rewrite_rule [@{thm HTTgen_def}] @{thm HTT_coinduct3}

fun HTT_coinduct3_tac ctxt s i =
res_inst_tac ctxt [(("R", 0), s)] @{thm HTT_coinduct3} i

val HTTgenIs =
map (mk_genIs @{theory} @{thms data_defs} @{thm HTTgenXH} @{thm HTTgen_mono})
["true : HTTgen(R)",
"false : HTTgen(R)",
"[| a : R;  b : R |] ==> <a,b> : HTTgen(R)",
"[| !!x. b(x) : R |] ==> lam x. b(x) : HTTgen(R)",
"one : HTTgen(R)",
"a : lfp(%x. HTTgen(x) Un R Un HTT) ==> inl(a) : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))",
"b : lfp(%x. HTTgen(x) Un R Un HTT) ==> inr(b) : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))",
"zero : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))",
"n : lfp(%x. HTTgen(x) Un R Un HTT) ==> succ(n) : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))",
"[] : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))",
"[| h : lfp(%x. HTTgen(x) Un R Un HTT); t : lfp(%x. HTTgen(x) Un R Un HTT) |] ==> h\$t : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))"]
*}

ML {* bind_thms ("HTTgenIs", HTTgenIs) *}

subsection {* Formation Rules for Types *}

lemma UnitF: "Unit <= HTT"
by (simp add: subsetXH UnitXH HTT_rews)

lemma BoolF: "Bool <= HTT"
by (fastsimp simp: subsetXH BoolXH iff: HTT_rews)

lemma PlusF: "[| A <= HTT;  B <= HTT |] ==> A + B  <= HTT"
by (fastsimp simp: subsetXH PlusXH iff: HTT_rews)

lemma SigmaF: "[| A <= HTT;  !!x. x:A ==> B(x) <= HTT |] ==> SUM x:A. B(x) <= HTT"
by (fastsimp simp: subsetXH SgXH HTT_rews)

(*** Formation Rules for Recursive types - using coinduction these only need ***)
(***                                          exhaution rule for type-former ***)

(*Proof by induction - needs induction rule for type*)
lemma "Nat <= HTT"
apply clarify
apply (erule Nat_ind)
apply (fastsimp iff: HTT_rews)+
done

lemma NatF: "Nat <= HTT"
apply clarify
apply (erule HTT_coinduct3)
apply (fast intro: HTTgenIs elim!: HTTgen_mono [THEN ci3_RI] dest: NatXH [THEN iffD1])
done

lemma ListF: "A <= HTT ==> List(A) <= HTT"
apply clarify
apply (erule HTT_coinduct3)
apply (fast intro!: HTTgenIs elim!: HTTgen_mono [THEN ci3_RI]
subsetD [THEN HTTgen_mono [THEN ci3_AI]]
dest: ListXH [THEN iffD1])
done

lemma ListsF: "A <= HTT ==> Lists(A) <= HTT"
apply clarify
apply (erule HTT_coinduct3)
apply (fast intro!: HTTgenIs elim!: HTTgen_mono [THEN ci3_RI]
subsetD [THEN HTTgen_mono [THEN ci3_AI]] dest: ListsXH [THEN iffD1])
done

lemma IListsF: "A <= HTT ==> ILists(A) <= HTT"
apply clarify
apply (erule HTT_coinduct3)
apply (fast intro!: HTTgenIs elim!: HTTgen_mono [THEN ci3_RI]
subsetD [THEN HTTgen_mono [THEN ci3_AI]] dest: IListsXH [THEN iffD1])
done

end
```