src/HOL/Tools/Presburger/presburger.ML

abstraction over functions is no default any more.

(*  Title:      HOL/Integ/presburger.ML
    ID:         $Id$
    Author:     Amine Chaieb and Stefan Berghofer, TU Muenchen
    License:    GPL (GNU GENERAL PUBLIC LICENSE)

Tactic for solving arithmetical Goals in Presburger Arithmetic
*)

(* This version of presburger deals with occurences of functional symbols in the subgoal and abstract over them to try to prove the more general formula. It then resolves with the subgoal. To enable this feature call the procedure with the parameter abs
*)

signature PRESBURGER = 
sig
 val presburger_tac : bool -> bool -> int -> tactic
 val presburger_method : bool -> bool -> int -> Proof.method
 val setup : (theory -> theory) list
 val trace : bool ref
end;

structure Presburger: PRESBURGER =
struct

val trace = ref false;
fun trace_msg s = if !trace then tracing s else ();

(*-----------------------------------------------------------------*)
(*cooper_pp: provefunction for the one-exstance quantifier elimination*)
(* Here still only one problem : The proof for the arithmetical transformations done on the dvd atomic formulae*)
(*-----------------------------------------------------------------*)

val presburger_ss = simpset_of (theory "Presburger");

fun cooper_pp sg (fm as e$Abs(xn,xT,p)) = 
  let val (xn1,p1) = variant_abs (xn,xT,p)
  in (CooperProof.cooper_prv sg (Free (xn1, xT)) p1) end;

fun mnnf_pp sg fm = CooperProof.proof_of_cnnf sg fm
  (CooperProof.proof_of_evalc sg);

fun tmproof_of_int_qelim sg fm =
  Qelim.tproof_of_mlift_qelim sg CooperDec.is_arith_rel
    (CooperProof.proof_of_linform sg) (mnnf_pp sg) (cooper_pp sg) fm;


(* Theorems to be used in this tactic*)

val zdvd_int = thm "zdvd_int";
val zdiff_int_split = thm "zdiff_int_split";
val all_nat = thm "all_nat";
val ex_nat = thm "ex_nat";
val number_of1 = thm "number_of1";
val number_of2 = thm "number_of2";
val split_zdiv = thm "split_zdiv";
val split_zmod = thm "split_zmod";
val mod_div_equality' = thm "mod_div_equality'";
val split_div' = thm "split_div'";
val Suc_plus1 = thm "Suc_plus1";
val imp_le_cong = thm "imp_le_cong";
val conj_le_cong = thm "conj_le_cong";

(* extract all the constants in a term*)
fun add_term_typed_consts (Const (c, T), cs) = (c,T) ins cs
  | add_term_typed_consts (t $ u, cs) =
      add_term_typed_consts (t, add_term_typed_consts (u, cs))
  | add_term_typed_consts (Abs (_, _, t), cs) = add_term_typed_consts (t, cs)
  | add_term_typed_consts (_, cs) = cs;

fun term_typed_consts t = add_term_typed_consts(t,[]);

(* Some Types*)
val bT = HOLogic.boolT;
val iT = HOLogic.intT;
val binT = HOLogic.binT;
val nT = HOLogic.natT;

(* Allowed Consts in formulae for presburger tactic*)

val allowed_consts =
  [("All", (iT --> bT) --> bT),
   ("Ex", (iT --> bT) --> bT),
   ("All", (nT --> bT) --> bT),
   ("Ex", (nT --> bT) --> bT),

   ("op &", bT --> bT --> bT),
   ("op |", bT --> bT --> bT),
   ("op -->", bT --> bT --> bT),
   ("op =", bT --> bT --> bT),
   ("Not", bT --> bT),

   ("op <=", iT --> iT --> bT),
   ("op =", iT --> iT --> bT),
   ("op <", iT --> iT --> bT),
   ("Divides.op dvd", iT --> iT --> bT),
   ("Divides.op div", iT --> iT --> iT),
   ("Divides.op mod", iT --> iT --> iT),
   ("op +", iT --> iT --> iT),
   ("op -", iT --> iT --> iT),
   ("op *", iT --> iT --> iT), 
   ("HOL.abs", iT --> iT),
   ("uminus", iT --> iT),
   ("HOL.max", iT --> iT --> iT),
   ("HOL.min", iT --> iT --> iT),

   ("op <=", nT --> nT --> bT),
   ("op =", nT --> nT --> bT),
   ("op <", nT --> nT --> bT),
   ("Divides.op dvd", nT --> nT --> bT),
   ("Divides.op div", nT --> nT --> nT),
   ("Divides.op mod", nT --> nT --> nT),
   ("op +", nT --> nT --> nT),
   ("op -", nT --> nT --> nT),
   ("op *", nT --> nT --> nT), 
   ("Suc", nT --> nT),
   ("HOL.max", nT --> nT --> nT),
   ("HOL.min", nT --> nT --> nT),

   ("Numeral.bin.Bit", binT --> bT --> binT),
   ("Numeral.bin.Pls", binT),
   ("Numeral.bin.Min", binT),
   ("Numeral.number_of", binT --> iT),
   ("Numeral.number_of", binT --> nT),
   ("0", nT),
   ("0", iT),
   ("1", nT),
   ("1", iT),
   ("False", bT),
   ("True", bT)];

(* Preparation of the formula to be sent to the Integer quantifier *)
(* elimination procedure                                           *)
(* Transforms meta implications and meta quantifiers to object     *)
(* implications and object quantifiers                             *)


(*==================================*)
(* Abstracting on subterms  ========*)
(*==================================*)
(* Returns occurences of terms that are function application of type int or nat*)

fun getfuncs fm = case strip_comb fm of
    (Free (_, T), ts as _ :: _) =>
      if body_type T mem [iT, nT] 
         andalso not (ts = []) andalso forall (null o loose_bnos) ts 
      then [fm]
      else foldl op union ([], map getfuncs ts)
  | (Var (_, T), ts as _ :: _) =>
      if body_type T mem [iT, nT] 
         andalso not (ts = []) andalso forall (null o loose_bnos) ts then [fm]
      else foldl op union ([], map getfuncs ts)
  | (Const (s, T), ts) =>
      if (s, T) mem allowed_consts orelse not (body_type T mem [iT, nT])
      then foldl op union ([], map getfuncs ts)
      else [fm]
  | (Abs (s, T, t), _) => getfuncs t
  | _ => [];


fun abstract_pres sg fm = 
  foldr (fn (t, u) =>
      let val T = fastype_of t
      in all T $ Abs ("x", T, abstract_over (t, u)) end)
         (getfuncs fm, fm);



(* hasfuncs_on_bounds dont care of the type of the functions applied!
 It returns true if there is a subterm coresponding to the application of
 a function on a bounded variable.

 Function applications are allowed only for well predefined functions a 
 consts*)

fun has_free_funcs fm  = case strip_comb fm of
    (Free (_, T), ts as _ :: _) => 
      if (body_type T mem [iT,nT]) andalso (not (T mem [iT,nT]))
      then true
      else exists (fn x => x) (map has_free_funcs ts)
  | (Var (_, T), ts as _ :: _) =>
      if (body_type T mem [iT,nT]) andalso not (T mem [iT,nT])
      then true
      else exists (fn x => x) (map has_free_funcs ts)
  | (Const (s, T), ts) =>  exists (fn x => x) (map has_free_funcs ts)
  | (Abs (s, T, t), _) => has_free_funcs t
  |_ => false;


(*returns true if the formula is relevant for presburger arithmetic tactic
The constants occuring in term t should be a subset of the allowed_consts
 There also should be no occurences of application of functions on bounded 
 variables. Whenever this function will be used, it will be ensured that t 
 will not contain subterms with function symbols that could have been 
 abstracted over.*)
 
fun relevant ps t = (term_typed_consts t) subset allowed_consts andalso 
  map (fn i => snd (nth_elem (i, ps))) (loose_bnos t) @
  map (snd o dest_Free) (term_frees t) @ map (snd o dest_Var) (term_vars t)
  subset [iT, nT]
  andalso not (has_free_funcs t);


fun prepare_for_presburger sg q fm = 
  let
    val ps = Logic.strip_params fm
    val hs = map HOLogic.dest_Trueprop (Logic.strip_assums_hyp fm)
    val c = HOLogic.dest_Trueprop (Logic.strip_assums_concl fm)
    val _ = if relevant (rev ps) c then () 
               else  (trace_msg ("Conclusion is not a presburger term:\n" ^
             Sign.string_of_term sg c); raise CooperDec.COOPER)
    fun mk_all ((s, T), (P,n)) =
      if 0 mem loose_bnos P then
        (HOLogic.all_const T $ Abs (s, T, P), n)
      else (incr_boundvars ~1 P, n-1)
    fun mk_all2 (v, t) = HOLogic.all_const (fastype_of v) $ lambda v t;
    val (rhs,irhs) = partition (relevant (rev ps)) hs
    val np = length ps
    val (fm',np) =  foldr (fn ((x, T), (fm,n)) => mk_all ((x, T), (fm,n)))
      (ps,(foldr HOLogic.mk_imp (rhs, c), np))
    val (vs, _) = partition (fn t => q orelse (type_of t) = nT)
      (term_frees fm' @ term_vars fm');
    val fm2 = foldr mk_all2 (vs, fm')
  in (fm2, np + length vs, length rhs) end;

(*Object quantifier to meta --*)
fun spec_step n th = if (n=0) then th else (spec_step (n-1) th) RS spec ;

(* object implication to meta---*)
fun mp_step n th = if (n=0) then th else (mp_step (n-1) th) RS mp;

(* the presburger tactic*)

(* Parameters : q = flag for quantify ofer free variables ; 
                a = flag for abstracting over function occurences
                i = subgoal  *)

fun presburger_tac q a i = ObjectLogic.atomize_tac i THEN (fn st =>
  let
    val g = BasisLibrary.List.nth (prems_of st, i - 1)
    val sg = sign_of_thm st
    (* The Abstraction step *)
    val g' = if a then abstract_pres sg g else g
    (* Transform the term*)
    val (t,np,nh) = prepare_for_presburger sg q g'
    (* Some simpsets for dealing with mod div abs and nat*)
    val simpset0 = HOL_basic_ss
      addsimps [mod_div_equality', Suc_plus1]
      addsplits [split_zdiv, split_zmod, split_div', split_min, split_max]
    (* Simp rules for changing (n::int) to int n *)
    val simpset1 = HOL_basic_ss
      addsimps [nat_number_of_def, zdvd_int] @ map (fn r => r RS sym)
        [int_int_eq, zle_int, zless_int, zadd_int, zmult_int]
      addsplits [zdiff_int_split]
    (*simp rules for elimination of int n*)

    val simpset2 = HOL_basic_ss
      addsimps [nat_0_le, all_nat, ex_nat, number_of1, number_of2, int_0, int_1]
      addcongs [conj_le_cong, imp_le_cong]
    (* simp rules for elimination of abs *)
    val simpset3 = HOL_basic_ss addsplits [abs_split]
    val ct = cterm_of sg (HOLogic.mk_Trueprop t)
    (* Theorem for the nat --> int transformation *)
    val pre_thm = Seq.hd (EVERY
      [simp_tac simpset0 1,
       TRY (simp_tac simpset1 1), TRY (simp_tac simpset2 1),
       TRY (simp_tac simpset3 1), TRY (simp_tac presburger_ss 1)]
      (trivial ct))
    fun assm_tac i = REPEAT_DETERM_N nh (assume_tac i)
    (* The result of the quantifier elimination *)
    val (th, tac) = case (prop_of pre_thm) of
        Const ("==>", _) $ (Const ("Trueprop", _) $ t1) $ _ =>
          (trace_msg ("calling procedure with term:\n" ^
             Sign.string_of_term sg t1);
           ((tmproof_of_int_qelim sg (Pattern.eta_long [] t1) RS iffD2) RS pre_thm,
            assm_tac (i + 1) THEN (if q then I else TRY) (rtac TrueI i)))
      | _ => (pre_thm, assm_tac i)
  in (rtac (((mp_step nh) o (spec_step np)) th) i 
      THEN tac) st
  end handle Subscript => no_tac st | CooperDec.COOPER => no_tac st);

fun presburger_args meth =
 let val parse_flag = 
         Args.$$$ "no_quantify" >> K (apfst (K false))
      || Args.$$$ "abs" >> K (apsnd (K true));
 in
   Method.simple_args 
  (Scan.optional (Args.$$$ "(" |-- Args.list1 parse_flag --| Args.$$$ ")") [] >>
    curry (foldl op |>) (true, false))
    (fn (q,a) => fn _ => meth q a 1)
  end;

fun presburger_method q a i = Method.METHOD (fn facts =>
  Method.insert_tac facts 1 THEN presburger_tac q a i)

val setup =
  [Method.add_method ("presburger",
     presburger_args presburger_method,
     "decision procedure for Presburger arithmetic"),
   ArithTheoryData.map (fn {splits, inj_consts, discrete, presburger} =>
     {splits = splits, inj_consts = inj_consts, discrete = discrete,
      presburger = Some (presburger_tac true false)})];

end;

val presburger_tac = Presburger.presburger_tac true true;