src/Provers/quantifier1.ML

handle Pattern.MATCH, not arbitrary exceptions;
misc tuning, trying to reduce line length a bit;

(*  Title:      Provers/quantifier1
    ID:         $Id$
    Author:     Tobias Nipkow
    Copyright   1997  TU Munich

Simplification procedures for turning

            ? x. ... & x = t & ...
     into   ? x. x = t & ... & ...
     where the `? x. x = t &' in the latter formula must be eliminated
           by ordinary simplification. 

     and   ! x. (... & x = t & ...) --> P x
     into  ! x. x = t --> (... & ...) --> P x
     where the `!x. x=t -->' in the latter formula is eliminated
           by ordinary simplification.

     And analogously for t=x, but the eqn is not turned around!

     NB Simproc is only triggered by "!x. P(x) & P'(x) --> Q(x)";
        "!x. x=t --> P(x)" is covered by the congreunce rule for -->;
        "!x. t=x --> P(x)" must be taken care of by an ordinary rewrite rule.
        As must be "? x. t=x & P(x)".
        
     And similarly for the bounded quantifiers.

Gries etc call this the "1 point rules"

The above also works for !x1..xn. and ?x1..xn by moving the defined
qunatifier inside first, but not for nested bounded quantifiers.

For set comprehensions the basic permutations
      ... & x = t & ...  ->  x = t & (... & ...)
      ... & t = x & ...  ->  t = x & (... & ...)
are also exported.

To avoid looping, NONE is returned if the term cannot be rearranged,
esp if x=t/t=x sits at the front already.
*)

signature QUANTIFIER1_DATA =
sig
  (*abstract syntax*)
  val dest_eq: term -> (term*term*term)option
  val dest_conj: term -> (term*term*term)option
  val dest_imp:  term -> (term*term*term)option
  val conj: term
  val imp:  term
  (*rules*)
  val iff_reflection: thm (* P <-> Q ==> P == Q *)
  val iffI:  thm
  val iff_trans: thm
  val conjI: thm
  val conjE: thm
  val impI:  thm
  val mp:    thm
  val exI:   thm
  val exE:   thm
  val uncurry: thm (* P --> Q --> R ==> P & Q --> R *)
  val iff_allI: thm (* !!x. P x <-> Q x ==> (!x. P x) = (!x. Q x) *)
  val iff_exI: thm (* !!x. P x <-> Q x ==> (? x. P x) = (? x. Q x) *)
  val all_comm: thm (* (!x y. P x y) = (!y x. P x y) *)
  val ex_comm: thm (* (? x y. P x y) = (? y x. P x y) *)
end;

signature QUANTIFIER1 =
sig
  val prove_one_point_all_tac: tactic
  val prove_one_point_ex_tac: tactic
  val rearrange_all: theory -> simpset -> term -> thm option
  val rearrange_ex:  theory -> simpset -> term -> thm option
  val rearrange_ball: (simpset -> tactic) -> theory -> simpset -> term -> thm option
  val rearrange_bex:  (simpset -> tactic) -> theory -> simpset -> term -> thm option
  val rearrange_Coll: tactic -> theory -> simpset -> term -> thm option
end;

functor Quantifier1Fun(Data: QUANTIFIER1_DATA): QUANTIFIER1 =
struct

open Data;

(* FIXME: only test! *)
fun def xs eq =
  (case dest_eq eq of
     SOME(c,s,t) =>
       let val n = length xs
       in s = Bound n andalso not(loose_bvar1(t,n)) orelse
          t = Bound n andalso not(loose_bvar1(s,n)) end
   | NONE => false);

fun extract_conj fst xs t = case dest_conj t of NONE => NONE
    | SOME(conj,P,Q) =>
        (if def xs P then (if fst then NONE else SOME(xs,P,Q)) else
         if def xs Q then SOME(xs,Q,P) else
         (case extract_conj false xs P of
            SOME(xs,eq,P') => SOME(xs,eq, conj $ P' $ Q)
          | NONE => (case extract_conj false xs Q of
                       SOME(xs,eq,Q') => SOME(xs,eq,conj $ P $ Q')
                     | NONE => NONE)));

fun extract_imp fst xs t = case dest_imp t of NONE => NONE
    | SOME(imp,P,Q) => if def xs P then (if fst then NONE else SOME(xs,P,Q))
                       else (case extract_conj false xs P of
                               SOME(xs,eq,P') => SOME(xs, eq, imp $ P' $ Q)
                             | NONE => (case extract_imp false xs Q of
                                          NONE => NONE
                                        | SOME(xs,eq,Q') =>
                                            SOME(xs,eq,imp$P$Q')));

fun extract_quant extract q =
  let fun exqu xs ((qC as Const(qa,_)) $ Abs(x,T,Q)) =
            if qa = q then exqu ((qC,x,T)::xs) Q else NONE
        | exqu xs P = extract (null xs) xs P
  in exqu [] end;

fun prove_conv tac thy tu =
  Goal.prove (ProofContext.init thy) [] [] (Logic.mk_equals tu)
    (K (rtac iff_reflection 1 THEN tac));

fun qcomm_tac qcomm qI i = REPEAT_DETERM (rtac qcomm i THEN rtac qI i) 

(* Proves (? x0..xn. ... & x0 = t & ...) = (? x1..xn x0. x0 = t & ... & ...)
   Better: instantiate exI
*)
local
val excomm = ex_comm RS iff_trans
in
val prove_one_point_ex_tac = qcomm_tac excomm iff_exI 1 THEN rtac iffI 1 THEN
    ALLGOALS(EVERY'[etac exE, REPEAT_DETERM o (etac conjE), rtac exI,
                    DEPTH_SOLVE_1 o (ares_tac [conjI])])
end;

(* Proves (! x0..xn. (... & x0 = t & ...) --> P x0) =
          (! x1..xn x0. x0 = t --> (... & ...) --> P x0)
*)
local
val tac = SELECT_GOAL
          (EVERY1[REPEAT o (dtac uncurry), REPEAT o (rtac impI), etac mp,
                  REPEAT o (etac conjE), REPEAT o (ares_tac [conjI])])
val allcomm = all_comm RS iff_trans
in
val prove_one_point_all_tac =
      EVERY1[qcomm_tac allcomm iff_allI,rtac iff_allI, rtac iffI, tac, tac]
end

fun renumber l u (Bound i) = Bound(if i < l orelse i > u then i else
                                   if i=u then l else i+1)
  | renumber l u (s$t) = renumber l u s $ renumber l u t
  | renumber l u (Abs(x,T,t)) = Abs(x,T,renumber (l+1) (u+1) t)
  | renumber _ _ atom = atom;

fun quantify qC x T xs P =
  let fun quant [] P = P
        | quant ((qC,x,T)::xs) P = quant xs (qC $ Abs(x,T,P))
      val n = length xs
      val Q = if n=0 then P else renumber 0 n P
  in quant xs (qC $ Abs(x,T,Q)) end;

fun rearrange_all thy _ (F as (all as Const(q,_)) $ Abs(x,T, P)) =
     (case extract_quant extract_imp q P of
        NONE => NONE
      | SOME(xs,eq,Q) =>
          let val R = quantify all x T xs (imp $ eq $ Q)
          in SOME(prove_conv prove_one_point_all_tac thy (F,R)) end)
  | rearrange_all _ _ _ = NONE;

fun rearrange_ball tac thy ss (F as Ball $ A $ Abs(x,T,P)) =
     (case extract_imp true [] P of
        NONE => NONE
      | SOME(xs,eq,Q) => if not(null xs) then NONE else
          let val R = imp $ eq $ Q
          in SOME(prove_conv (tac ss) thy (F,Ball $ A $ Abs(x,T,R))) end)
  | rearrange_ball _ _ _ _ = NONE;

fun rearrange_ex thy _ (F as (ex as Const(q,_)) $ Abs(x,T,P)) =
     (case extract_quant extract_conj q P of
        NONE => NONE
      | SOME(xs,eq,Q) =>
          let val R = quantify ex x T xs (conj $ eq $ Q)
          in SOME(prove_conv prove_one_point_ex_tac thy (F,R)) end)
  | rearrange_ex _ _ _ = NONE;

fun rearrange_bex tac thy ss (F as Bex $ A $ Abs(x,T,P)) =
     (case extract_conj true [] P of
        NONE => NONE
      | SOME(xs,eq,Q) => if not(null xs) then NONE else
          SOME(prove_conv (tac ss) thy (F,Bex $ A $ Abs(x,T,conj$eq$Q))))
  | rearrange_bex _ _ _ _ = NONE;

fun rearrange_Coll tac thy _ (F as Coll $ Abs(x,T,P)) =
     (case extract_conj true [] P of
        NONE => NONE
      | SOME(_,eq,Q) =>
          let val R = Coll $ Abs(x,T, conj $ eq $ Q)
          in SOME(prove_conv tac thy (F,R)) end);

end;