Theory Wfd

(*  Title:      CCL/Wfd.thy
    Author:     Martin Coen, Cambridge University Computer Laboratory
    Copyright   1993  University of Cambridge
*)

section Well-founded relations in CCL

theory Wfd
imports Trancl Type Hered
begin

definition Wfd :: "[i set]  o"
  where "Wfd(R) == ALL P.(ALL x.(ALL y.<y,x> : R  y:P)  x:P)  (ALL a. a:P)"

definition wf :: "[i set]  i set"
  where "wf(R) == {x. x:R  Wfd(R)}"

definition wmap :: "[ii,i set]  i set"
  where "wmap(f,R) == {p. EX x y. p=<x,y>  <f(x),f(y)> : R}"

definition lex :: "[i set,i set] => i set"      (infixl "**" 70)
  where "ra**rb == {p. EX a a' b b'. p = <<a,b>,<a',b'>>  (<a,a'> : ra | (a=a'  <b,b'> : rb))}"

definition NatPR :: "i set"
  where "NatPR == {p. EX x:Nat. p=<x,succ(x)>}"

definition ListPR :: "i set  i set"
  where "ListPR(A) == {p. EX h:A. EX t:List(A). p=<t,h$t>}"


lemma wfd_induct:
  assumes 1: "Wfd(R)"
    and 2: "x. ALL y. <y,x>: R  P(y)  P(x)"
  shows "P(a)"
  apply (rule 1 [unfolded Wfd_def, rule_format, THEN CollectD])
  using 2 apply blast
  done

lemma wfd_strengthen_lemma:
  assumes 1: "x y.<x,y> : R  Q(x)"
    and 2: "ALL x. (ALL y. <y,x> : R  y : P)  x : P"
    and 3: "x. Q(x)  x:P"
  shows "a:P"
  apply (rule 2 [rule_format])
  using 1 3
  apply blast
  done

method_setup wfd_strengthen = 
  Scan.lift Parse.embedded_inner_syntax >> (fn s => fn ctxt =>
    SIMPLE_METHOD' (fn i =>
      Rule_Insts.res_inst_tac ctxt [((("Q", 0), Position.none), s)] [] @{thm wfd_strengthen_lemma} i
        THEN assume_tac ctxt (i + 1)))


lemma wf_anti_sym: "Wfd(r); <a,x>:r; <x,a>:r  P"
  apply (subgoal_tac "ALL x. <a,x>:r  <x,a>:r  P")
   apply blast
  apply (erule wfd_induct)
  apply blast
  done

lemma wf_anti_refl: "Wfd(r); <a,a>: r  P"
  apply (rule wf_anti_sym)
  apply assumption+
  done


subsection Irreflexive transitive closure

lemma trancl_wf:
  assumes 1: "Wfd(R)"
  shows "Wfd(R^+)"
  apply (unfold Wfd_def)
  apply (rule allI ballI impI)+
(*must retain the universal formula for later use!*)
  apply (rule allE, assumption)
  apply (erule mp)
  apply (rule 1 [THEN wfd_induct])
  apply (rule impI [THEN allI])
  apply (erule tranclE)
   apply blast
  apply (erule spec [THEN mp, THEN spec, THEN mp])
   apply assumption+
  done


subsection Lexicographic Ordering

lemma lexXH:
  "p : ra**rb  (EX a a' b b'. p = <<a,b>,<a',b'>>  (<a,a'> : ra | a=a'  <b,b'> : rb))"
  unfolding lex_def by blast

lemma lexI1: "<a,a'> : ra  <<a,b>,<a',b'>> : ra**rb"
  by (blast intro!: lexXH [THEN iffD2])

lemma lexI2: "<b,b'> : rb  <<a,b>,<a,b'>> : ra**rb"
  by (blast intro!: lexXH [THEN iffD2])

lemma lexE:
  assumes 1: "p : ra**rb"
    and 2: "a a' b b'. <a,a'> : ra; p=<<a,b>,<a',b'>>  R"
    and 3: "a b b'. <b,b'> : rb; p = <<a,b>,<a,b'>>  R"
  shows R
  apply (rule 1 [THEN lexXH [THEN iffD1], THEN exE])
  using 2 3
  apply blast
  done

lemma lex_pair: "p : r**s; a a' b b'. p = <<a,b>,<a',b'>>  P P"
  apply (erule lexE)
   apply blast+
  done

lemma lex_wf:
  assumes 1: "Wfd(R)"
    and 2: "Wfd(S)"
  shows "Wfd(R**S)"
  apply (unfold Wfd_def)
  apply safe
  apply (wfd_strengthen "λx. EX a b. x=<a,b>")
   apply (blast elim!: lex_pair)
  apply (subgoal_tac "ALL a b.<a,b>:P")
   apply blast
  apply (rule 1 [THEN wfd_induct, THEN allI])
  apply (rule 2 [THEN wfd_induct, THEN allI]) back
  apply (fast elim!: lexE)
  done


subsection Mapping

lemma wmapXH: "p : wmap(f,r)  (EX x y. p=<x,y>  <f(x),f(y)> : r)"
  unfolding wmap_def by blast

lemma wmapI: "<f(a),f(b)> : r  <a,b> : wmap(f,r)"
  by (blast intro!: wmapXH [THEN iffD2])

lemma wmapE: "p : wmap(f,r); a b. <f(a),f(b)> : r; p=<a,b>  R  R"
  by (blast dest!: wmapXH [THEN iffD1])

lemma wmap_wf:
  assumes 1: "Wfd(r)"
  shows "Wfd(wmap(f,r))"
  apply (unfold Wfd_def)
  apply clarify
  apply (subgoal_tac "ALL b. ALL a. f (a) = b  a:P")
   apply blast
  apply (rule 1 [THEN wfd_induct, THEN allI])
  apply clarify
  apply (erule spec [THEN mp])
  apply (safe elim!: wmapE)
  apply (erule spec [THEN mp, THEN spec, THEN mp])
   apply assumption
   apply (rule refl)
  done


subsection Projections

lemma wfstI: "<xa,ya> : r  <<xa,xb>,<ya,yb>> : wmap(fst,r)"
  apply (rule wmapI)
  apply simp
  done

lemma wsndI: "<xb,yb> : r  <<xa,xb>,<ya,yb>> : wmap(snd,r)"
  apply (rule wmapI)
  apply simp
  done

lemma wthdI: "<xc,yc> : r  <<xa,<xb,xc>>,<ya,<yb,yc>>> : wmap(thd,r)"
  apply (rule wmapI)
  apply simp
  done


subsection Ground well-founded relations

lemma wfI: "Wfd(r);  a : r  a : wf(r)"
  unfolding wf_def by blast

lemma Empty_wf: "Wfd({})"
  unfolding Wfd_def by (blast elim: EmptyXH [THEN iffD1, THEN FalseE])

lemma wf_wf: "Wfd(wf(R))"
  unfolding wf_def
  apply (rule_tac Q = "Wfd(R)" in excluded_middle [THEN disjE])
   apply simp_all
  apply (rule Empty_wf)
  done

lemma NatPRXH: "p : NatPR  (EX x:Nat. p=<x,succ(x)>)"
  unfolding NatPR_def by blast

lemma ListPRXH: "p : ListPR(A)  (EX h:A. EX t:List(A).p=<t,h$t>)"
  unfolding ListPR_def by blast

lemma NatPRI: "x : Nat  <x,succ(x)> : NatPR"
  by (auto simp: NatPRXH)

lemma ListPRI: "t : List(A); h : A  <t,h $ t> : ListPR(A)"
  by (auto simp: ListPRXH)

lemma NatPR_wf: "Wfd(NatPR)"
  apply (unfold Wfd_def)
  apply clarify
  apply (wfd_strengthen "λx. x:Nat")
   apply (fastforce iff: NatPRXH)
  apply (erule Nat_ind)
   apply (fastforce iff: NatPRXH)+
  done

lemma ListPR_wf: "Wfd(ListPR(A))"
  apply (unfold Wfd_def)
  apply clarify
  apply (wfd_strengthen "λx. x:List (A)")
   apply (fastforce iff: ListPRXH)
  apply (erule List_ind)
   apply (fastforce iff: ListPRXH)+
  done


subsection General Recursive Functions

lemma letrecT:
  assumes 1: "a : A"
    and 2: "p g. p:A; ALL x:{x: A. <x,p>:wf(R)}. g(x) : D(x)  h(p,g) : D(p)"
  shows "letrec g x be h(x,g) in g(a) : D(a)"
  apply (rule 1 [THEN rev_mp])
  apply (rule wf_wf [THEN wfd_induct])
  apply (subst letrecB)
  apply (rule impI)
  apply (erule 2)
  apply blast
  done

lemma SPLITB: "SPLIT(<a,b>,B) = B(a,b)"
  unfolding SPLIT_def
  apply (rule set_ext)
  apply blast
  done

lemma letrec2T:
  assumes "a : A"
    and "b : B"
    and "p q g. p:A; q:B;
              ALL x:A. ALL y:{y: B. <<x,y>,<p,q>>:wf(R)}. g(x,y) : D(x,y)  
                h(p,q,g) : D(p,q)"
  shows "letrec g x y be h(x,y,g) in g(a,b) : D(a,b)"
  apply (unfold letrec2_def)
  apply (rule SPLITB [THEN subst])
  apply (assumption | rule letrecT pairT splitT assms)+
  apply (subst SPLITB)
  apply (assumption | rule ballI SubtypeI assms)+
  apply (rule SPLITB [THEN subst])
  apply (assumption | rule letrecT SubtypeI pairT splitT assms |
    erule bspec SubtypeE sym [THEN subst])+
  done

lemma lem: "SPLIT(<a,<b,c>>,λx xs. SPLIT(xs,λy z. B(x,y,z))) = B(a,b,c)"
  by (simp add: SPLITB)

lemma letrec3T:
  assumes "a : A"
    and "b : B"
    and "c : C"
    and "p q r g. p:A; q:B; r:C;
       ALL x:A. ALL y:B. ALL z:{z:C. <<x,<y,z>>,<p,<q,r>>> : wf(R)}.
                                                        g(x,y,z) : D(x,y,z)  
                h(p,q,r,g) : D(p,q,r)"
  shows "letrec g x y z be h(x,y,z,g) in g(a,b,c) : D(a,b,c)"
  apply (unfold letrec3_def)
  apply (rule lem [THEN subst])
  apply (assumption | rule letrecT pairT splitT assms)+
  apply (simp add: SPLITB)
  apply (assumption | rule ballI SubtypeI assms)+
  apply (rule lem [THEN subst])
  apply (assumption | rule letrecT SubtypeI pairT splitT assms |
    erule bspec SubtypeE sym [THEN subst])+
  done

lemmas letrecTs = letrecT letrec2T letrec3T


subsection Type Checking for Recursive Calls

lemma rcallT:
  "ALL x:{x:A.<x,p>:wf(R)}.g(x):D(x);  
    g(a) : D(a)  g(a) : E;  a:A;  <a,p>:wf(R)  g(a) : E"
  by blast

lemma rcall2T:
  "ALL x:A. ALL y:{y:B.<<x,y>,<p,q>>:wf(R)}.g(x,y):D(x,y);
    g(a,b) : D(a,b)  g(a,b) : E; a:A; b:B; <<a,b>,<p,q>>:wf(R)  g(a,b) : E"
  by blast

lemma rcall3T:
  "ALL x:A. ALL y:B. ALL z:{z:C.<<x,<y,z>>,<p,<q,r>>>:wf(R)}. g(x,y,z):D(x,y,z);
    g(a,b,c) : D(a,b,c)  g(a,b,c) : E;
    a:A; b:B; c:C; <<a,<b,c>>,<p,<q,r>>> : wf(R)  g(a,b,c) : E"
  by blast

lemmas rcallTs = rcallT rcall2T rcall3T


subsection Instantiating an induction hypothesis with an equality assumption

lemma hyprcallT:
  assumes 1: "g(a) = b"
    and 2: "ALL x:{x:A.<x,p>:wf(R)}.g(x):D(x)"
    and 3: "ALL x:{x:A.<x,p>:wf(R)}.g(x):D(x)  b=g(a)  g(a) : D(a)  P"
    and 4: "ALL x:{x:A.<x,p>:wf(R)}.g(x):D(x)  a:A"
    and 5: "ALL x:{x:A.<x,p>:wf(R)}.g(x):D(x)  <a,p>:wf(R)"
  shows P
  apply (rule 3 [OF 2, OF 1 [symmetric]])
  apply (rule rcallT [OF 2])
    apply assumption
   apply (rule 4 [OF 2])
  apply (rule 5 [OF 2])
  done

lemma hyprcall2T:
  assumes 1: "g(a,b) = c"
    and 2: "ALL x:A. ALL y:{y:B.<<x,y>,<p,q>>:wf(R)}.g(x,y):D(x,y)"
    and 3: "c = g(a,b); g(a,b) : D(a,b)  P"
    and 4: "a:A"
    and 5: "b:B"
    and 6: "<<a,b>,<p,q>>:wf(R)"
  shows P
  apply (rule 3)
    apply (rule 1 [symmetric])
  apply (rule rcall2T)
      apply (rule 2)
     apply assumption
    apply (rule 4)
   apply (rule 5)
  apply (rule 6)
  done

lemma hyprcall3T:
  assumes 1: "g(a,b,c) = d"
    and 2: "ALL x:A. ALL y:B. ALL z:{z:C.<<x,<y,z>>,<p,<q,r>>>:wf(R)}.g(x,y,z):D(x,y,z)"
    and 3: "d = g(a,b,c); g(a,b,c) : D(a,b,c)  P"
    and 4: "a:A"
    and 5: "b:B"
    and 6: "c:C"
    and 7: "<<a,<b,c>>,<p,<q,r>>> : wf(R)"
  shows P
  apply (rule 3)
   apply (rule 1 [symmetric])
  apply (rule rcall3T)
       apply (rule 2)
      apply assumption
     apply (rule 4)
    apply (rule 5)
   apply (rule 6)
  apply (rule 7)
  done

lemmas hyprcallTs = hyprcallT hyprcall2T hyprcall3T


subsection Rules to Remove Induction Hypotheses after Type Checking

lemma rmIH1: "ALL x:{x:A.<x,p>:wf(R)}.g(x):D(x); P  P" .

lemma rmIH2: "ALL x:A. ALL y:{y:B.<<x,y>,<p,q>>:wf(R)}.g(x,y):D(x,y); P  P" .
  
lemma rmIH3:
 "ALL x:A. ALL y:B. ALL z:{z:C.<<x,<y,z>>,<p,<q,r>>>:wf(R)}.g(x,y,z):D(x,y,z); P  P" .

lemmas rmIHs = rmIH1 rmIH2 rmIH3


subsection Lemmas for constructors and subtypes

(* 0-ary constructors do not need additional rules as they are handled *)
(*                                      correctly by applying SubtypeI *)

lemma Subtype_canTs:
  "a b A B P. a : {x:A. b:{y:B(a).P(<x,y>)}}  <a,b> : {x:Sigma(A,B).P(x)}"
  "a A B P. a : {x:A. P(inl(x))}  inl(a) : {x:A+B. P(x)}"
  "b A B P. b : {x:B. P(inr(x))}  inr(b) : {x:A+B. P(x)}"
  "a P. a : {x:Nat. P(succ(x))}  succ(a) : {x:Nat. P(x)}"
  "h t A P. h : {x:A. t : {y:List(A).P(x$y)}}  h$t : {x:List(A).P(x)}"
  by (assumption | rule SubtypeI canTs icanTs | erule SubtypeE)+

lemma letT: "f(t):B; ¬t=bot  let x be t in f(x) : B"
  apply (erule letB [THEN ssubst])
  apply assumption
  done

lemma applyT2: "a:A; f : Pi(A,B)  f ` a  : B(a)"
  apply (erule applyT)
  apply assumption
  done

lemma rcall_lemma1: "a:A; a:A  P(a)  a : {x:A. P(x)}"
  by blast

lemma rcall_lemma2: "a:{x:A. Q(x)}; a:A; Q(a)  P(a)  a : {x:A. P(x)}"
  by blast

lemmas rcall_lemmas = asm_rl rcall_lemma1 SubtypeD1 rcall_lemma2


subsection Typechecking

ML 
local

val type_rls =
  @{thms canTs} @ @{thms icanTs} @ @{thms applyT2} @ @{thms ncanTs} @ @{thms incanTs} @
  @{thms precTs} @ @{thms letrecTs} @ @{thms letT} @ @{thms Subtype_canTs};

fun bvars Const_Pure.all _ for Abs(s,_,t) l = bvars t (s::l)
  | bvars _ l = l

fun get_bno l n Const_Pure.all _ for Abs(s,_,t) = get_bno (s::l) n t
  | get_bno l n Const_Trueprop for t = get_bno l n t
  | get_bno l n Const_Ball _ for _ Abs(s,_,t) = get_bno (s::l) (n+1) t
  | get_bno l n Const_mem _ for t _ = get_bno l n t
  | get_bno l n (t $ s) = get_bno l n t
  | get_bno l n (Bound m) = (m-length(l),n)

(* Not a great way of identifying induction hypothesis! *)
fun could_IH x = Term.could_unify(x,hd (Thm.prems_of @{thm rcallT})) orelse
                 Term.could_unify(x,hd (Thm.prems_of @{thm rcall2T})) orelse
                 Term.could_unify(x,hd (Thm.prems_of @{thm rcall3T}))

fun IHinst tac rls = SUBGOAL (fn (Bi,i) =>
  let val bvs = bvars Bi []
      val ihs = filter could_IH (Logic.strip_assums_hyp Bi)
      val rnames = map (fn x =>
                    let val (a,b) = get_bno [] 0 x
                    in (nth bvs a, b) end) ihs
      fun try_IHs [] = no_tac
        | try_IHs ((x,y)::xs) =
            tac [((("g", 0), Position.none), x)] (nth rls (y - 1)) i ORELSE (try_IHs xs)
  in try_IHs rnames end)

fun is_rigid_prog t =
  (case (Logic.strip_assums_concl t) of
    Const_Trueprop for Const_mem _ for a _ => null (Term.add_vars a [])
  | _ => false)

in

fun rcall_tac ctxt i =
  let fun tac ps rl i = Rule_Insts.res_inst_tac ctxt ps [] rl i THEN assume_tac ctxt i
  in IHinst tac @{thms rcallTs} i end
  THEN eresolve_tac ctxt @{thms rcall_lemmas} i

fun raw_step_tac ctxt prems i =
  assume_tac ctxt i ORELSE
  resolve_tac ctxt (prems @ type_rls) i ORELSE
  rcall_tac ctxt i ORELSE
  ematch_tac ctxt @{thms SubtypeE} i ORELSE
  match_tac ctxt @{thms SubtypeI} i

fun tc_step_tac ctxt prems = SUBGOAL (fn (Bi,i) =>
    if is_rigid_prog Bi then raw_step_tac ctxt prems i else no_tac)

fun typechk_tac ctxt rls i = SELECT_GOAL (REPEAT_FIRST (tc_step_tac ctxt rls)) i


(*** Clean up Correctness Condictions ***)

fun clean_ccs_tac ctxt =
  let fun tac ps rl i = Rule_Insts.eres_inst_tac ctxt ps [] rl i THEN assume_tac ctxt i in
    TRY (REPEAT_FIRST (IHinst tac @{thms hyprcallTs} ORELSE'
      eresolve_tac ctxt ([asm_rl, @{thm SubtypeE}] @ @{thms rmIHs}) ORELSE'
      hyp_subst_tac ctxt))
  end

fun gen_ccs_tac ctxt rls i =
  SELECT_GOAL (REPEAT_FIRST (tc_step_tac ctxt rls) THEN clean_ccs_tac ctxt) i

end


method_setup typechk = 
  Attrib.thms >> (fn ths => fn ctxt => SIMPLE_METHOD' (typechk_tac ctxt ths))


method_setup clean_ccs = 
  Scan.succeed (SIMPLE_METHOD o clean_ccs_tac)


method_setup gen_ccs = 
  Attrib.thms >> (fn ths => fn ctxt => SIMPLE_METHOD' (gen_ccs_tac ctxt ths))



subsection Evaluation

named_theorems eval "evaluation rules"

ML 
fun eval_tac ths =
  Subgoal.FOCUS_PREMS (fn {context = ctxt, prems, ...} =>
    let val eval_rules = Named_Theorems.get ctxt named_theorems‹eval›
    in DEPTH_SOLVE_1 (resolve_tac ctxt (ths @ prems @ rev eval_rules) 1) end)


method_setup eval = 
  Attrib.thms >> (fn ths => fn ctxt => SIMPLE_METHOD' (CHANGED o eval_tac ths ctxt))



lemmas eval_rls [eval] = trueV falseV pairV lamV caseVtrue caseVfalse caseVpair caseVlam

lemma applyV [eval]:
  assumes "f  lam x. b(x)"
    and "b(a)  c"
  shows "f ` a  c"
  unfolding apply_def by (eval assms)

lemma letV:
  assumes 1: "t  a"
    and 2: "f(a)  c"
  shows "let x be t in f(x)  c"
  apply (unfold let_def)
  apply (rule 1 [THEN canonical])
  apply (tactic 
    REPEAT (DEPTH_SOLVE_1 (resolve_tac context (@{thms assms} @ @{thms eval_rls}) 1 ORELSE
      eresolve_tac context @{thms substitute} 1)))
  done

lemma fixV: "f(fix(f))  c  fix(f)  c"
  apply (unfold fix_def)
  apply (rule applyV)
   apply (rule lamV)
  apply assumption
  done

lemma letrecV:
  "h(t,λy. letrec g x be h(x,g) in g(y))  c   
                 letrec g x be h(x,g) in g(t)  c"
  apply (unfold letrec_def)
  apply (assumption | rule fixV applyV  lamV)+
  done

lemmas [eval] = letV letrecV fixV

lemma V_rls [eval]:
  "true  true"
  "false  false"
  "b c t u. btrue; tc  if b then t else u  c"
  "b c t u. bfalse; uc  if b then t else u  c"
  "a b. <a,b>  <a,b>"
  "a b c t h. t  <a,b>; h(a,b)  c  split(t,h)  c"
  "zero  zero"
  "n. succ(n)  succ(n)"
  "c n t u. n  zero; t  c  ncase(n,t,u)  c"
  "c n t u x. n  succ(x); u(x)  c  ncase(n,t,u)  c"
  "c n t u. n  zero; t  c  nrec(n,t,u)  c"
  "c n t u x. nsucc(x); u(x,nrec(x,t,u))c  nrec(n,t,u)c"
  "[]  []"
  "h t. h$t  h$t"
  "c l t u. l  []; t  c  lcase(l,t,u)  c"
  "c l t u x xs. l  x$xs; u(x,xs)  c  lcase(l,t,u)  c"
  "c l t u. l  []; t  c  lrec(l,t,u)  c"
  "c l t u x xs. lx$xs; u(x,xs,lrec(xs,t,u))c  lrec(l,t,u)c"
  unfolding data_defs by eval+


subsection Factorial

schematic_goal
  "letrec f n be ncase(n,succ(zero),λx. nrec(n,zero,λy g. nrec(f(x),g,λz h. succ(h))))  
   in f(succ(succ(zero)))  ?a"
  by eval

schematic_goal
  "letrec f n be ncase(n,succ(zero),λx. nrec(n,zero,λy g. nrec(f(x),g,λz h. succ(h))))  
   in f(succ(succ(succ(zero))))  ?a"
  by eval

subsection Less Than Or Equal

schematic_goal
  "letrec f p be split(p,λm n. ncase(m,true,λx. ncase(n,false,λy. f(<x,y>))))
   in f(<succ(zero), succ(zero)>)  ?a"
  by eval

schematic_goal
  "letrec f p be split(p,λm n. ncase(m,true,λx. ncase(n,false,λy. f(<x,y>))))
   in f(<succ(zero), succ(succ(succ(succ(zero))))>)  ?a"
  by eval

schematic_goal
  "letrec f p be split(p,λm n. ncase(m,true,λx. ncase(n,false,λy. f(<x,y>))))
   in f(<succ(succ(succ(succ(succ(zero))))), succ(succ(succ(succ(zero))))>)  ?a"
  by eval


subsection Reverse

schematic_goal
  "letrec id l be lcase(l,[],λx xs. x$id(xs))  
   in id(zero$succ(zero)$[])  ?a"
  by eval

schematic_goal
  "letrec rev l be lcase(l,[],λx xs. lrec(rev(xs),x$[],λy ys g. y$g))  
   in rev(zero$succ(zero)$(succ((lam x. x)`succ(zero)))$([]))  ?a"
  by eval

end