solver.ml 13.4 KB
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(*-----------------------------------------------------------------------
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** Copyright (C) 2001, 2002 - Verimag.
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** This file may only be copied under the terms of the GNU Library General
** Public License 
**-----------------------------------------------------------------------
**
** File: solver.ml
** Main author: jahier@imag.fr
*)

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open List
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open Formula
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open Env_state
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open Util
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open Hashtbl
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(****************************************************************************)
	  
let (formula_list_to_conj: formula list -> formula) =
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  fun fl -> 
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    (** Transform a (non-empty) list of formula to the conjunction
       made of those formula.  
    *)
    match fl with
	[] -> assert false
      | f::[] -> f
      | f1::f2::tail -> 
          List.fold_left (fun x y -> And(x, y)) (And(f1, f2)) tail

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let rec (formula_to_bdd : formula -> Bdd.t) =
  fun f ->
    (** Transform the formula [f] into a bdd. Also tabulates the
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      result in the [bdd_tbl] field of [env_state] because this
      translation is expensive.
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    *)
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    try Hashtbl.find env_state.bdd_tbl f
    with Not_found -> 
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      let bdd =
	match f with 
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	    Not(f1) ->     Bdd.dnot (formula_to_bdd f1)
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	  | Or(f1, f2) ->  Bdd.dor  (formula_to_bdd f1) (formula_to_bdd f2)
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	  | And(f1, f2) -> Bdd.dand (formula_to_bdd f1) (formula_to_bdd f2)
	      
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	  | True ->        Bdd.dtrue env_state.bdd_manager
	  | False ->       Bdd.dfalse env_state.bdd_manager
	  | Bvar(vn) ->    Bdd.ithvar env_state.bdd_manager (Env_state.atomic_formula_to_index f)
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	  | Eq(e1, e2) -> 
	      (* We transform [e1 = e2] into [e1 <= e2 ^ e1 >= e2] as the 
		 numeric solver can not handle disequalities *)
	      ( Bdd.dand 
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		  (Bdd.ithvar env_state.bdd_manager (Env_state.atomic_formula_to_index (SupEq(e1, e2))))
		  (Bdd.ithvar env_state.bdd_manager (Env_state.atomic_formula_to_index (InfEq(e1, e2)))) )
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	  | Neq(e1, e2) -> 
	      (* We transform [e1 <> e2] into [e1 < e2 ^ e1 > e2] as the 
		 numeric solver can not handle disequalities *)
	      ( Bdd.dand 
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		  (Bdd.ithvar env_state.bdd_manager (Env_state.atomic_formula_to_index (Sup(e1, e2))))
		  (Bdd.ithvar env_state.bdd_manager (Env_state.atomic_formula_to_index (Inf(e1, e2)))) )
	  | SupEq(e1, e2) ->  Bdd.ithvar env_state.bdd_manager (Env_state.atomic_formula_to_index f)
	  | Sup(e1, e2)   ->  Bdd.ithvar env_state.bdd_manager (Env_state.atomic_formula_to_index f)
	  | InfEq(e1, e2) ->  Bdd.ithvar env_state.bdd_manager (Env_state.atomic_formula_to_index f)
	  | Inf(e1, e2)   ->  Bdd.ithvar env_state.bdd_manager (Env_state.atomic_formula_to_index f)
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      in
      let _ = match f with 
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	  Not(nf) -> ()
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	| _  -> Hashtbl.add env_state.bdd_tbl (Not(f)) (Bdd.dnot bdd) 
      in
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	(*      print_string ("$$$ building the bdd of " 
		^ (formula_to_string f) ^ "\n") ; *)
	(*	flush stdout ; *)
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	Hashtbl.add env_state.bdd_tbl f bdd;
	bdd
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(****************************************************************************)
(****************************************************************************)


(* Exported *)
let rec (is_satisfiable: formula list -> bool) = 
  fun fl -> 
    let f = formula_list_to_conj fl in
    let bdd = formula_to_bdd (formula_list_to_conj fl) in
      not (Bdd.is_false bdd) &&
      ( 
	try 
	  let (n, m) = find env_state.snt bdd in 
	    not ((zero_sol, zero_sol) = (n, m))
	with Not_found -> true
      )
      


(****************************************************************************)
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(****************************************************************************)

type var = int

(** In the following, we call a comb the bdd of a conjunction of
 litterals (var). They provide the ordering in which litterals
 appear in the bdds we manipulate.
*)

let rec (count_missing_vars: Bdd.t -> var -> int -> Bdd.t * int) =
  fun comb var cpt -> 
    (* Returns [cpt] + the number of variables occurring in [comb]
       before reaching [var] ([var] excluded). Also returns the comb
       which topvar is [var]. *)
    let _ = assert (not (Bdd.is_cst comb)) in
    let combvar = Bdd.topvar comb in
      if var = combvar
      then (comb, cpt)
      else count_missing_vars (Bdd.dthen comb) var (cpt+1)


let rec (build_sol_nb_table: Bdd.t -> Bdd.t -> sol_nb * sol_nb) =
  fun bdd comb -> 
    (** Returns the relative (to which bbd points to it) number of
      solutions of [bdd] and the one of its negation. Also udpates
      the solution number table [env_state.snt] for [bdd] and its
      negation, and recursively for all its sub-bdds. 
    *)
    let bdd_not = (Bdd.dnot bdd) in
    let (sol_nb, sol_nb_not) =
      try
	let (nt, ne) = Hashtbl.find env_state.snt bdd 
	and (not_nt, not_ne) = Hashtbl.find env_state.snt bdd_not in
	  (* solutions numbers in the table are absolute *)
	  ((add_sol_nb nt ne), (add_sol_nb not_nt not_ne))
      with Not_found ->  	
	let _ = assert (not (Bdd.is_cst bdd)) in
	let (nt, not_nt) = compute_absolute_sol_nb (Bdd.dthen bdd) comb in
	let (ne, not_ne) = compute_absolute_sol_nb (Bdd.delse bdd) comb in
	  Hashtbl.add env_state.snt bdd (nt, ne) ;
	  Hashtbl.add env_state.snt bdd_not (not_nt, not_ne) ; 
	  ((add_sol_nb nt ne), (add_sol_nb not_nt not_ne))
    in
      (sol_nb, sol_nb_not)
and 
  (compute_absolute_sol_nb: Bdd.t -> Bdd.t -> sol_nb * sol_nb) =
  fun sub_bdd comb -> 
    (* returns the absolute number of solutions of [sub_bdd] (and its
       negation) w.r.t. [comb], where [comb] is the comb of the
       father of [sub_bdd]. *)
    if Bdd.is_cst sub_bdd 
    then 
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      let sol_nb = 
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	if Bdd.is_true comb (* iff no bool are to be gen *)
	then one_sol
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	else (two_power_of (List.length (Bdd.list_of_support (Bdd.dthen comb)))) 
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      in
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	if Bdd.is_true sub_bdd
	then (sol_nb, zero_sol) 
	else (zero_sol, sol_nb)
    else 
      let topvar = Bdd.topvar sub_bdd in
      let (sub_comb, missing_vars_nb) = 
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	if Bdd.is_true comb (* iff no bool are to be gen *)
	then (comb, 0)
	else count_missing_vars (Bdd.dthen comb) topvar 0 
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      in
      let (n0, not_n0) = build_sol_nb_table sub_bdd sub_comb in
      let factor = (two_power_of missing_vars_nb) in
	(mult_sol_nb n0 factor, mult_sol_nb not_n0 factor)
	
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(****************************************************************************)
(****************************************************************************)

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let (toss_up_one_var: var -> subst) =
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  fun var -> 
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    (* [var] is a index that ougth to correspond to a boolean
       variable. This fonction performs a toss and returns a
       substitution for the corresponding boolean variable. *)
    let af = Env_state.index_to_atomic_formula var in
    let vn = (
      match af with 
        Bvar(vn0) -> vn0
      | _  -> 
	  (* Only bool index ougth to appear in the comb. *)
	  assert false
    ) in
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    let ran = Random.float 1. in
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      if (ran < 0.5) 
      then (vn, Formula.Bool(true)) 
      else (vn, Formula.Bool(false))


let is_a_numeric_constraint af =
  match af with
      Bvar(_) -> false
    | _ -> true

(* exported *)
exception No_numeric_solution


let (formula_to_nc : formula -> Rnumsolver.nc) =
  fun f -> 
    match f with
	Sup(e1, e2)   -> Rnumsolver.Sup(e1, e2) 
      | SupEq(e1, e2) -> Rnumsolver.SupEq(e1, e2)
      | Inf(e1, e2)   -> Rnumsolver.Inf(e1, e2)
      | InfEq(e1, e2) -> Rnumsolver.InfEq(e1, e2)
      | _ -> assert false

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let rec (draw_in_bdd: subst list * Rnumsolver.store -> Bdd.t -> Bdd.t -> 
	   subst list * Rnumsolver.store) = 
  fun (sl, store) bdd comb ->
    (** Returns [sl] appended to a draw of all the boolean variables
      bigger than the topvar of [bdd] according to the ordering
      induced by the comb [comb]. Also returns the (non empty) store
      obtained by adding to [store] all the numeric constraints that
      were encountered during this draw.
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      Raises the [No_numeric_solution] exception whenever no valid
      path in [bdd] leads to a satisfiable set of numeric
      constraints.  
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    *)
    let _ = assert (not (Bdd.is_cst bdd)) in
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    let _ = assert (Hashtbl.mem env_state.snt bdd) in
    let bddvar  = Bdd.topvar bdd in
    let af = (Env_state.index_to_atomic_formula bddvar) in 
    let top_var_is_numeric = is_a_numeric_constraint af in
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      if
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	not(Bdd.is_true comb) && (* iff no bool are to be gen *)
	bddvar <> (Bdd.topvar comb) &&
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	not top_var_is_numeric
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      then
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	let new_sl = (toss_up_one_var (Bdd.topvar comb))::sl in
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	  draw_in_bdd (new_sl, store) bdd (Bdd.dthen comb)
      else 
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	(* bddvar = combvar xor top_var_is_numeric *) 
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	(* nb: I handle those two cases alltogether to avoid code
	   duplication (i.e., retrieving sol numbers, performing the
	   toss, the recursive call, handling the base case where a
	   dtrue bdd is reached, etc).  It makes the code a little
	   bit more obscur, but ...  *)
	let (n, m) = Hashtbl.find env_state.snt bdd in
	let _ =
	  if ((eq_sol_nb n zero_sol) && (eq_sol_nb m zero_sol))
	  then raise No_numeric_solution ;
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	in
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	let (store_plus_af, store_plus_not_af) = 
	  (* A first trick to avoid code dup (cf nb above) *)
	  if top_var_is_numeric
	  then 
	    Rnumsolver.split store (formula_to_nc af)
	  else 
	    (store, store)
	in
	let (swap, store1, bdd1, bool1, sol_nb1, store2, bdd2, bool2, sol_nb2) =
	  (* Depending on the result of a toss (based on the number
	     of solution in each branch), we try the [else] or the
	     [then] branch first. [swap] indicates whether or not the
	     [else] part is put before the [then] one. *)
	  let ran = Random.float 1. in
	    if ran < ((float_of_sol_nb n) /. (float_of_sol_nb (add_sol_nb n m)))
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	    then
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	      (false, store_plus_af, (Bdd.dthen bdd), true, n,
	       store_plus_not_af, (Bdd.delse bdd), false, m )
	    else 
	      (true, store_plus_not_af, (Bdd.delse bdd), false, m,
	       store_plus_af, (Bdd.dthen bdd), true, n )
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	in
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	let (sl1, sl2, new_comb) = (
	  (* A second trick to avoid code dup (cf nb above) *)
	  match af with 
	    Bvar(vn) -> 
	      (((vn, Formula.Bool(bool1))::sl), 
	       ((vn, Formula.Bool(bool2))::sl), 
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	       (if Bdd.is_true comb then comb else Bdd.dthen comb) )
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	  | _ -> 
	      (* top_var_is_numeric *)
	      (sl, sl, comb)
	  )
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	in
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	let res_opt =
	  (* A solution will be found in this branch iff there exists
	     at least one path in the bdd that leads to a satisfiable
	     set of numeric constraints. If it is not the case,
	     [res_opt] is bound to [None]. *)
	  if not (Rnumsolver.is_empty store1)
	  then 
	    try 
	      let tail_draw1 = 
		if Bdd.is_true bdd1
		then
		  (* Toss the remaining bool vars. *)
		  ( (List.append 
		       sl1 
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		       (map toss_up_one_var (Bdd.list_of_support new_comb))),
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		    store1
		  )
		else
		  draw_in_bdd (sl1, store1) bdd1 new_comb
	      in
		Some(tail_draw1)
	    with No_numeric_solution -> 
	      None
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	  else
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	    None
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	in
	  match res_opt with 
	      Some(res) -> res
	    | None -> 
		(* The second branch is now tried because no path in
		   the first bdd leaded to a satisfiable set of
		   numeric constraints. *)
		if not (eq_sol_nb sol_nb2 zero_sol)
		then
		  if not (Rnumsolver.is_empty store2)
		  then    
		    if Bdd.is_true bdd2
		    then 
		      ( (List.append 
			   sl2 
			   (List.map toss_up_one_var 
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			      (Bdd.list_of_support new_comb))),
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			store2
		      )
		    else
		      draw_in_bdd (sl2, store2) bdd2 new_comb 
		  else
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		    raise No_numeric_solution
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		else
		  raise No_numeric_solution
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let (draw : vn list -> vnt list -> Bdd.t -> Bdd.t -> subst list * subst list) =
  fun bool_vars_to_gen num_vnt_to_gen comb bdd ->
    (** Draw the output and local vars to be generated by the environnent. *)
    let (bool_subst_l, store) = 
      draw_in_bdd ([], (Rnumsolver.new_store num_vnt_to_gen)) bdd comb 
    in
    let num_subst_l = Rnumsolver.draw_inside store in
    let subst_l = append bool_subst_l num_subst_l in
    let (out_vars, _) = List.split (env_state.output_var_names) 
    in
      assert ( 
	(*  Checks that we generated all variables. *)
	let (gen_vars, _) = split subst_l in
	let (num_vars_to_gen, _) = split num_vnt_to_gen in
	let vars_to_gen = append bool_vars_to_gen num_vars_to_gen in
          (sort (compare) gen_vars) = (sort (compare) vars_to_gen) 
      );
      (* Splits output and local vars. *)
      List.partition 
	(fun (vn, _) -> List.mem vn out_vars) 
	subst_l
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(* Exported *)
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let (solve_formula: int -> formula list -> vn list -> vnt list ->
       (subst list * subst list) list) =
  fun p fl bool_vars_to_gen num_vars_to_gen ->
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    let f = formula_list_to_conj fl in
    let bdd = Hashtbl.find env_state.bdd_tbl f in
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    let bool_vars_to_gen_f = 
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      List.fold_left
	(fun acc vn -> (And(Bvar(vn), acc)))
	True
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	bool_vars_to_gen
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    in
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    let comb = formula_to_bdd bool_vars_to_gen_f in
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(* (**)    let _ = *)
(* (**)      (* XXX Recompute the solution number everytime as long as mldd sucks *) *)
(* (**)      begin *)
(* (**)	Hashtbl.clear env_state.snt ; *)
(* (**)	Hashtbl.add env_state.snt *)
(* (**)	  (Bdd.dtrue env_state.bdd_manager) (one_sol, zero_sol); *)
(* (**)	Hashtbl.add env_state.snt *)
(* (**)	  (Bdd.dfalse env_state.bdd_manager) (zero_sol, one_sol) *)
(* (**)      end *)
(* (**)    in *)
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    let _ =
      if not (Hashtbl.mem env_state.snt bdd)
      then
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	let rec skip_var comb v =
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	  if Bdd.is_true comb (* iff no bool are to be gen *)
	  then comb
	  else 
	    let topvar = (Bdd.topvar comb) in
	      if v = topvar then comb else skip_var (Bdd.dthen comb) v
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	in
	let comb2 = skip_var comb (Bdd.topvar bdd) in
	  build_sol_nb_table bdd comb2 
      else
	(zero_sol, zero_sol)
    in
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      try Util.unfold (draw bool_vars_to_gen num_vars_to_gen comb) bdd p
      with No_numeric_solution -> 
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	Hashtbl.replace env_state.snt bdd (zero_sol, zero_sol);
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	[]
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