(* Manipulations over terms *)

type term =
    Var of int
  | Prop of head * term list
and head =
    { name: string;
      mutable props: (term * term) list }

let rec print_term = function
    Var v ->
      print_string "v"; print_int v
  | Prop (head,argl) ->
      print_string "(";
      print_string head.name;
      List.iter (fun t -> print_string " "; print_term t) argl;
      print_string ")"
			 
let lemmas = ref ([] : head list)

(* Replacement for property lists *)

let get name =
  let rec get_rec = function
    hd1::hdl ->
      if hd1.name = name then hd1 else get_rec hdl
  | [] ->
      let entry = {name = name; props = []} in
        lemmas := entry :: !lemmas;
        entry
  in get_rec !lemmas

let add_lemma (Prop(_, [(Prop(headl,_) as left); right])) =
  headl.props <- (left, right) :: headl.props

(* Substitutions *)

type subst = Bind of int * term

let get_binding v list =
  let rec get_rec = function
    [] -> failwith "unbound"
  | Bind(w,t)::rest -> if v = w  then t else get_rec rest
  in get_rec list

let apply_subst alist term =
  let rec as_rec = function
     Var v -> begin try get_binding v alist with Failure _ -> term end
   | Prop (head,argl) -> Prop (head, List.map as_rec argl)
  in as_rec term

exception Unify

let rec unify (term1, term2) =
  unify1 (term1, term2, [])

and unify1 (term1, term2, unify_subst) =
 match term2 with
    Var v ->
      begin try
        if get_binding v unify_subst = term1
        then unify_subst
        else raise Unify
      with Failure _ ->
        Bind(v,term1) :: unify_subst
      end
  | Prop (head2, argl2) ->
      match term1 with
         Var _ -> raise Unify
       | Prop (head1,argl1) ->
           if head1 == head2
           then unify1_lst (argl1, argl2, unify_subst)
           else raise Unify

and unify1_lst = function
    ([], [], unify_subst) -> unify_subst
  | (h1::r1, h2::r2, unify_subst) ->
      unify1_lst(r1, r2, unify1(h1, h2, unify_subst))
  | _ -> raise Unify


let rec rewrite = function
    Var _ as term -> term
  | Prop (head, argl) ->
      rewrite_with_lemmas (Prop (head, List.map rewrite argl),  head.props)
and rewrite_with_lemmas = function
    (term, []) ->
      term
  | (term, (t1,t2)::rest) ->
      try
        rewrite (apply_subst (unify (term, t1)) t2)
      with Unify ->
        rewrite_with_lemmas (term, rest)

type cterm = CVar of int | CProp of string * cterm list

let rec cterm_to_term = function
    CVar v -> Var v
  | CProp(p, l) -> Prop(get p, List.map cterm_to_term l)

let add t = add_lemma (cterm_to_term t)

let _ =
add (CProp
("equal",
 [CProp ("compile",[CVar 5]); 
  CProp
  ("reverse",
   [CProp ("codegen",[CProp ("optimize",[CVar 5]); CProp ("nil",[])])])]));
add (CProp
("equal",
 [CProp ("eqp",[CVar 23; CVar 24]); 
  CProp ("equal",[CProp ("fix",[CVar 23]); CProp ("fix",[CVar 24])])]));
add (CProp
("equal",
 [CProp ("gt",[CVar 23; CVar 24]); CProp ("lt",[CVar 24; CVar 23])]));
add (CProp
("equal",
 [CProp ("le",[CVar 23; CVar 24]); CProp ("ge",[CVar 24; CVar 23])]));
add (CProp
("equal",
 [CProp ("ge",[CVar 23; CVar 24]); CProp ("le",[CVar 24; CVar 23])]));
add (CProp
("equal",
 [CProp ("boolean",[CVar 23]); 
  CProp
  ("or",
   [CProp ("equal",[CVar 23; CProp ("true",[])]); 
    CProp ("equal",[CVar 23; CProp ("false",[])])])]));
add (CProp
("equal",
 [CProp ("iff",[CVar 23; CVar 24]); 
  CProp
  ("and",
   [CProp ("implies",[CVar 23; CVar 24]); 
    CProp ("implies",[CVar 24; CVar 23])])]));
add (CProp
("equal",
 [CProp ("even1",[CVar 23]); 
  CProp
  ("if",
   [CProp ("zerop",[CVar 23]); CProp ("true",[]); 
    CProp ("odd",[CProp ("sub1",[CVar 23])])])]));
add (CProp
("equal",
 [CProp ("countps_",[CVar 11; CVar 15]); 
  CProp ("countps_loop",[CVar 11; CVar 15; CProp ("zero",[])])]));
add (CProp
("equal",
 [CProp ("fact_",[CVar 8]); 
  CProp ("fact_loop",[CVar 8; CProp ("one",[])])]));
add (CProp
("equal",
 [CProp ("reverse_",[CVar 23]); 
  CProp ("reverse_loop",[CVar 23; CProp ("nil",[])])]));
add (CProp
("equal",
 [CProp ("divides",[CVar 23; CVar 24]); 
  CProp ("zerop",[CProp ("remainder",[CVar 24; CVar 23])])]));
add (CProp
("equal",
 [CProp ("assume_true",[CVar 21; CVar 0]); 
  CProp ("cons",[CProp ("cons",[CVar 21; CProp ("true",[])]); CVar 0])]));
add (CProp
("equal",
 [CProp ("assume_false",[CVar 21; CVar 0]); 
  CProp ("cons",[CProp ("cons",[CVar 21; CProp ("false",[])]); CVar 0])]));
add (CProp
("equal",
 [CProp ("tautology_checker",[CVar 23]); 
  CProp ("tautologyp",[CProp ("normalize",[CVar 23]); CProp ("nil",[])])]));
add (CProp
("equal",
 [CProp ("falsify",[CVar 23]); 
  CProp ("falsify1",[CProp ("normalize",[CVar 23]); CProp ("nil",[])])]));
add (CProp
("equal",
 [CProp ("prime",[CVar 23]); 
  CProp
  ("and",
   [CProp ("not",[CProp ("zerop",[CVar 23])]); 
    CProp
    ("not",
     [CProp ("equal",[CVar 23; CProp ("add1",[CProp ("zero",[])])])]); 
    CProp ("prime1",[CVar 23; CProp ("sub1",[CVar 23])])])]));
add (CProp
("equal",
 [CProp ("and",[CVar 15; CVar 16]); 
  CProp
  ("if",
   [CVar 15; 
    CProp ("if",[CVar 16; CProp ("true",[]); CProp ("false",[])]); 
    CProp ("false",[])])]));
add (CProp
("equal",
 [CProp ("or",[CVar 15; CVar 16]); 
  CProp
  ("if",
   [CVar 15; CProp ("true",[]); 
    CProp ("if",[CVar 16; CProp ("true",[]); CProp ("false",[])]); 
    CProp ("false",[])])]));
add (CProp
("equal",
 [CProp ("not",[CVar 15]); 
  CProp ("if",[CVar 15; CProp ("false",[]); CProp ("true",[])])]));
add (CProp
("equal",
 [CProp ("implies",[CVar 15; CVar 16]); 
  CProp
  ("if",
   [CVar 15; 
    CProp ("if",[CVar 16; CProp ("true",[]); CProp ("false",[])]); 
    CProp ("true",[])])]));
add (CProp
("equal",
 [CProp ("fix",[CVar 23]); 
  CProp ("if",[CProp ("numberp",[CVar 23]); CVar 23; CProp ("zero",[])])]));
add (CProp
("equal",
 [CProp ("if",[CProp ("if",[CVar 0; CVar 1; CVar 2]); CVar 3; CVar 4]); 
  CProp
  ("if",
   [CVar 0; CProp ("if",[CVar 1; CVar 3; CVar 4]); 
    CProp ("if",[CVar 2; CVar 3; CVar 4])])]));
add (CProp
("equal",
 [CProp ("zerop",[CVar 23]); 
  CProp
  ("or",
   [CProp ("equal",[CVar 23; CProp ("zero",[])]); 
    CProp ("not",[CProp ("numberp",[CVar 23])])])]));
add (CProp
("equal",
 [CProp ("plus",[CProp ("plus",[CVar 23; CVar 24]); CVar 25]); 
  CProp ("plus",[CVar 23; CProp ("plus",[CVar 24; CVar 25])])]));
add (CProp
("equal",
 [CProp ("equal",[CProp ("plus",[CVar 0; CVar 1]); CProp ("zero",[])]); 
  CProp ("and",[CProp ("zerop",[CVar 0]); CProp ("zerop",[CVar 1])])]));
add (CProp
("equal",[CProp ("difference",[CVar 23; CVar 23]); CProp ("zero",[])]));
add (CProp
("equal",
 [CProp
  ("equal",
   [CProp ("plus",[CVar 0; CVar 1]); CProp ("plus",[CVar 0; CVar 2])]); 
  CProp ("equal",[CProp ("fix",[CVar 1]); CProp ("fix",[CVar 2])])]));
add (CProp
("equal",
 [CProp
  ("equal",[CProp ("zero",[]); CProp ("difference",[CVar 23; CVar 24])]); 
  CProp ("not",[CProp ("gt",[CVar 24; CVar 23])])]));
add (CProp
("equal",
 [CProp ("equal",[CVar 23; CProp ("difference",[CVar 23; CVar 24])]); 
  CProp
  ("and",
   [CProp ("numberp",[CVar 23]); 
    CProp
    ("or",
     [CProp ("equal",[CVar 23; CProp ("zero",[])]); 
      CProp ("zerop",[CVar 24])])])]));
add (CProp
("equal",
 [CProp
  ("meaning",
   [CProp ("plus_tree",[CProp ("append",[CVar 23; CVar 24])]); CVar 0]); 
  CProp
  ("plus",
   [CProp ("meaning",[CProp ("plus_tree",[CVar 23]); CVar 0]); 
    CProp ("meaning",[CProp ("plus_tree",[CVar 24]); CVar 0])])]));
add (CProp
("equal",
 [CProp
  ("meaning",
   [CProp ("plus_tree",[CProp ("plus_fringe",[CVar 23])]); CVar 0]); 
  CProp ("fix",[CProp ("meaning",[CVar 23; CVar 0])])]));
add (CProp
("equal",
 [CProp ("append",[CProp ("append",[CVar 23; CVar 24]); CVar 25]); 
  CProp ("append",[CVar 23; CProp ("append",[CVar 24; CVar 25])])]));
add (CProp
("equal",
 [CProp ("reverse",[CProp ("append",[CVar 0; CVar 1])]); 
  CProp
  ("append",[CProp ("reverse",[CVar 1]); CProp ("reverse",[CVar 0])])]));
add (CProp
("equal",
 [CProp ("times",[CVar 23; CProp ("plus",[CVar 24; CVar 25])]); 
  CProp
  ("plus",
   [CProp ("times",[CVar 23; CVar 24]); 
    CProp ("times",[CVar 23; CVar 25])])]));
add (CProp
("equal",
 [CProp ("times",[CProp ("times",[CVar 23; CVar 24]); CVar 25]); 
  CProp ("times",[CVar 23; CProp ("times",[CVar 24; CVar 25])])]));
add (CProp
("equal",
 [CProp
  ("equal",[CProp ("times",[CVar 23; CVar 24]); CProp ("zero",[])]); 
  CProp ("or",[CProp ("zerop",[CVar 23]); CProp ("zerop",[CVar 24])])]));
add (CProp
("equal",
 [CProp ("exec",[CProp ("append",[CVar 23; CVar 24]); CVar 15; CVar 4]); 
  CProp
  ("exec",[CVar 24; CProp ("exec",[CVar 23; CVar 15; CVar 4]); CVar 4])]));
add (CProp
("equal",
 [CProp ("mc_flatten",[CVar 23; CVar 24]); 
  CProp ("append",[CProp ("flatten",[CVar 23]); CVar 24])]));
add (CProp
("equal",
 [CProp ("member",[CVar 23; CProp ("append",[CVar 0; CVar 1])]); 
  CProp
  ("or",
   [CProp ("member",[CVar 23; CVar 0]); 
    CProp ("member",[CVar 23; CVar 1])])]));
add (CProp
("equal",
 [CProp ("member",[CVar 23; CProp ("reverse",[CVar 24])]); 
  CProp ("member",[CVar 23; CVar 24])]));
add (CProp
("equal",
 [CProp ("length",[CProp ("reverse",[CVar 23])]); 
  CProp ("length",[CVar 23])]));
add (CProp
("equal",
 [CProp ("member",[CVar 0; CProp ("intersect",[CVar 1; CVar 2])]); 
  CProp
  ("and",
   [CProp ("member",[CVar 0; CVar 1]); CProp ("member",[CVar 0; CVar 2])])]));
add (CProp
("equal",[CProp ("nth",[CProp ("zero",[]); CVar 8]); CProp ("zero",[])]));
add (CProp
("equal",
 [CProp ("exp",[CVar 8; CProp ("plus",[CVar 9; CVar 10])]); 
  CProp
  ("times",
   [CProp ("exp",[CVar 8; CVar 9]); CProp ("exp",[CVar 8; CVar 10])])]));
add (CProp
("equal",
 [CProp ("exp",[CVar 8; CProp ("times",[CVar 9; CVar 10])]); 
  CProp ("exp",[CProp ("exp",[CVar 8; CVar 9]); CVar 10])]));
add (CProp
("equal",
 [CProp ("reverse_loop",[CVar 23; CVar 24]); 
  CProp ("append",[CProp ("reverse",[CVar 23]); CVar 24])]));
add (CProp
("equal",
 [CProp ("reverse_loop",[CVar 23; CProp ("nil",[])]); 
  CProp ("reverse",[CVar 23])]));
add (CProp
("equal",
 [CProp ("count_list",[CVar 25; CProp ("sort_lp",[CVar 23; CVar 24])]); 
  CProp
  ("plus",
   [CProp ("count_list",[CVar 25; CVar 23]); 
    CProp ("count_list",[CVar 25; CVar 24])])]));
add (CProp
("equal",
 [CProp
  ("equal",
   [CProp ("append",[CVar 0; CVar 1]); CProp ("append",[CVar 0; CVar 2])]); 
  CProp ("equal",[CVar 1; CVar 2])]));
add (CProp
("equal",
 [CProp
  ("plus",
   [CProp ("remainder",[CVar 23; CVar 24]); 
    CProp ("times",[CVar 24; CProp ("quotient",[CVar 23; CVar 24])])]); 
  CProp ("fix",[CVar 23])]));
add (CProp
("equal",
 [CProp
  ("power_eval",[CProp ("big_plus",[CVar 11; CVar 8; CVar 1]); CVar 1]); 
  CProp ("plus",[CProp ("power_eval",[CVar 11; CVar 1]); CVar 8])]));
add (CProp
("equal",
 [CProp
  ("power_eval",
   [CProp ("big_plus",[CVar 23; CVar 24; CVar 8; CVar 1]); CVar 1]); 
  CProp
  ("plus",
   [CVar 8; 
    CProp
    ("plus",
     [CProp ("power_eval",[CVar 23; CVar 1]); 
      CProp ("power_eval",[CVar 24; CVar 1])])])]));
add (CProp
("equal",
 [CProp ("remainder",[CVar 24; CProp ("one",[])]); CProp ("zero",[])]));
add (CProp
("equal",
 [CProp ("lt",[CProp ("remainder",[CVar 23; CVar 24]); CVar 24]); 
  CProp ("not",[CProp ("zerop",[CVar 24])])]));
add (CProp
("equal",[CProp ("remainder",[CVar 23; CVar 23]); CProp ("zero",[])]));
add (CProp
("equal",
 [CProp ("lt",[CProp ("quotient",[CVar 8; CVar 9]); CVar 8]); 
  CProp
  ("and",
   [CProp ("not",[CProp ("zerop",[CVar 8])]); 
    CProp
    ("or",
     [CProp ("zerop",[CVar 9]); 
      CProp ("not",[CProp ("equal",[CVar 9; CProp ("one",[])])])])])]));
add (CProp
("equal",
 [CProp ("lt",[CProp ("remainder",[CVar 23; CVar 24]); CVar 23]); 
  CProp
  ("and",
   [CProp ("not",[CProp ("zerop",[CVar 24])]); 
    CProp ("not",[CProp ("zerop",[CVar 23])]); 
    CProp ("not",[CProp ("lt",[CVar 23; CVar 24])])])]));
add (CProp
("equal",
 [CProp ("power_eval",[CProp ("power_rep",[CVar 8; CVar 1]); CVar 1]); 
  CProp ("fix",[CVar 8])]));
add (CProp
("equal",
 [CProp
  ("power_eval",
   [CProp
    ("big_plus",
     [CProp ("power_rep",[CVar 8; CVar 1]); 
      CProp ("power_rep",[CVar 9; CVar 1]); CProp ("zero",[]); 
      CVar 1]); 
    CVar 1]); 
  CProp ("plus",[CVar 8; CVar 9])]));
add (CProp
("equal",
 [CProp ("gcd",[CVar 23; CVar 24]); CProp ("gcd",[CVar 24; CVar 23])]));
add (CProp
("equal",
 [CProp ("nth",[CProp ("append",[CVar 0; CVar 1]); CVar 8]); 
  CProp
  ("append",
   [CProp ("nth",[CVar 0; CVar 8]); 
    CProp
    ("nth",
     [CVar 1; CProp ("difference",[CVar 8; CProp ("length",[CVar 0])])])])]));
add (CProp
("equal",
 [CProp ("difference",[CProp ("plus",[CVar 23; CVar 24]); CVar 23]); 
  CProp ("fix",[CVar 24])]));
add (CProp
("equal",
 [CProp ("difference",[CProp ("plus",[CVar 24; CVar 23]); CVar 23]); 
  CProp ("fix",[CVar 24])]));
add (CProp
("equal",
 [CProp
  ("difference",
   [CProp ("plus",[CVar 23; CVar 24]); CProp ("plus",[CVar 23; CVar 25])]); 
  CProp ("difference",[CVar 24; CVar 25])]));
add (CProp
("equal",
 [CProp ("times",[CVar 23; CProp ("difference",[CVar 2; CVar 22])]); 
  CProp
  ("difference",
   [CProp ("times",[CVar 2; CVar 23]); 
    CProp ("times",[CVar 22; CVar 23])])]));
add (CProp
("equal",
 [CProp ("remainder",[CProp ("times",[CVar 23; CVar 25]); CVar 25]); 
  CProp ("zero",[])]));
add (CProp
("equal",
 [CProp
  ("difference",
   [CProp ("plus",[CVar 1; CProp ("plus",[CVar 0; CVar 2])]); CVar 0]); 
  CProp ("plus",[CVar 1; CVar 2])]));
add (CProp
("equal",
 [CProp
  ("difference",
   [CProp ("add1",[CProp ("plus",[CVar 24; CVar 25])]); CVar 25]); 
  CProp ("add1",[CVar 24])]));
add (CProp
("equal",
 [CProp
  ("lt",
   [CProp ("plus",[CVar 23; CVar 24]); CProp ("plus",[CVar 23; CVar 25])]); 
  CProp ("lt",[CVar 24; CVar 25])]));
add (CProp
("equal",
 [CProp
  ("lt",
   [CProp ("times",[CVar 23; CVar 25]); 
    CProp ("times",[CVar 24; CVar 25])]); 
  CProp
  ("and",
   [CProp ("not",[CProp ("zerop",[CVar 25])]); 
    CProp ("lt",[CVar 23; CVar 24])])]));
add (CProp
("equal",
 [CProp ("lt",[CVar 24; CProp ("plus",[CVar 23; CVar 24])]); 
  CProp ("not",[CProp ("zerop",[CVar 23])])]));
add (CProp
("equal",
 [CProp
  ("gcd",
   [CProp ("times",[CVar 23; CVar 25]); 
    CProp ("times",[CVar 24; CVar 25])]); 
  CProp ("times",[CVar 25; CProp ("gcd",[CVar 23; CVar 24])])]));
add (CProp
("equal",
 [CProp ("value",[CProp ("normalize",[CVar 23]); CVar 0]); 
  CProp ("value",[CVar 23; CVar 0])]));
add (CProp
("equal",
 [CProp
  ("equal",
   [CProp ("flatten",[CVar 23]); 
    CProp ("cons",[CVar 24; CProp ("nil",[])])]); 
  CProp
  ("and",
   [CProp ("nlistp",[CVar 23]); CProp ("equal",[CVar 23; CVar 24])])]));
add (CProp
("equal",
 [CProp ("listp",[CProp ("gother",[CVar 23])]); 
  CProp ("listp",[CVar 23])]));
add (CProp
("equal",
 [CProp ("samefringe",[CVar 23; CVar 24]); 
  CProp
  ("equal",[CProp ("flatten",[CVar 23]); CProp ("flatten",[CVar 24])])]));
add (CProp
("equal",
 [CProp
  ("equal",
   [CProp ("greatest_factor",[CVar 23; CVar 24]); CProp ("zero",[])]); 
  CProp
  ("and",
   [CProp
    ("or",
     [CProp ("zerop",[CVar 24]); 
      CProp ("equal",[CVar 24; CProp ("one",[])])]); 
    CProp ("equal",[CVar 23; CProp ("zero",[])])])]));
add (CProp
("equal",
 [CProp
  ("equal",
   [CProp ("greatest_factor",[CVar 23; CVar 24]); CProp ("one",[])]); 
  CProp ("equal",[CVar 23; CProp ("one",[])])]));
add (CProp
("equal",
 [CProp ("numberp",[CProp ("greatest_factor",[CVar 23; CVar 24])]); 
  CProp
  ("not",
   [CProp
    ("and",
     [CProp
      ("or",
       [CProp ("zerop",[CVar 24]); 
        CProp ("equal",[CVar 24; CProp ("one",[])])]); 
      CProp ("not",[CProp ("numberp",[CVar 23])])])])]));
add (CProp
("equal",
 [CProp ("times_list",[CProp ("append",[CVar 23; CVar 24])]); 
  CProp
  ("times",
   [CProp ("times_list",[CVar 23]); CProp ("times_list",[CVar 24])])]));
add (CProp
("equal",
 [CProp ("prime_list",[CProp ("append",[CVar 23; CVar 24])]); 
  CProp
  ("and",
   [CProp ("prime_list",[CVar 23]); CProp ("prime_list",[CVar 24])])]));
add (CProp
("equal",
 [CProp ("equal",[CVar 25; CProp ("times",[CVar 22; CVar 25])]); 
  CProp
  ("and",
   [CProp ("numberp",[CVar 25]); 
    CProp
    ("or",
     [CProp ("equal",[CVar 25; CProp ("zero",[])]); 
      CProp ("equal",[CVar 22; CProp ("one",[])])])])]));
add (CProp
("equal",
 [CProp ("ge",[CVar 23; CVar 24]); 
  CProp ("not",[CProp ("lt",[CVar 23; CVar 24])])]));
add (CProp
("equal",
 [CProp ("equal",[CVar 23; CProp ("times",[CVar 23; CVar 24])]); 
  CProp
  ("or",
   [CProp ("equal",[CVar 23; CProp ("zero",[])]); 
    CProp
    ("and",
     [CProp ("numberp",[CVar 23]); 
      CProp ("equal",[CVar 24; CProp ("one",[])])])])]));
add (CProp
("equal",
 [CProp ("remainder",[CProp ("times",[CVar 24; CVar 23]); CVar 24]); 
  CProp ("zero",[])]));
add (CProp
("equal",
 [CProp ("equal",[CProp ("times",[CVar 0; CVar 1]); CProp ("one",[])]); 
  CProp
  ("and",
   [CProp ("not",[CProp ("equal",[CVar 0; CProp ("zero",[])])]); 
    CProp ("not",[CProp ("equal",[CVar 1; CProp ("zero",[])])]); 
    CProp ("numberp",[CVar 0]); CProp ("numberp",[CVar 1]); 
    CProp ("equal",[CProp ("sub1",[CVar 0]); CProp ("zero",[])]); 
    CProp ("equal",[CProp ("sub1",[CVar 1]); CProp ("zero",[])])])]));
add (CProp
("equal",
 [CProp
  ("lt",
   [CProp ("length",[CProp ("delete",[CVar 23; CVar 11])]); 
    CProp ("length",[CVar 11])]); 
  CProp ("member",[CVar 23; CVar 11])]));
add (CProp
("equal",
 [CProp ("sort2",[CProp ("delete",[CVar 23; CVar 11])]); 
  CProp ("delete",[CVar 23; CProp ("sort2",[CVar 11])])]));
add (CProp ("equal",[CProp ("dsort",[CVar 23]); CProp ("sort2",[CVar 23])]));
add (CProp
("equal",
 [CProp
  ("length",
   [CProp
    ("cons",
     [CVar 0; 
      CProp
      ("cons",
       [CVar 1; 
        CProp
        ("cons",
         [CVar 2; 
          CProp
          ("cons",
           [CVar 3; 
            CProp ("cons",[CVar 4; CProp ("cons",[CVar 5; CVar 6])])])])])])])
  ; CProp ("plus",[CProp ("six",[]); CProp ("length",[CVar 6])])]));
add (CProp
("equal",
 [CProp
  ("difference",
   [CProp ("add1",[CProp ("add1",[CVar 23])]); CProp ("two",[])]); 
  CProp ("fix",[CVar 23])]));
add (CProp
("equal",
 [CProp
  ("quotient",
   [CProp ("plus",[CVar 23; CProp ("plus",[CVar 23; CVar 24])]); 
    CProp ("two",[])]); 
  CProp
  ("plus",[CVar 23; CProp ("quotient",[CVar 24; CProp ("two",[])])])]));
add (CProp
("equal",
 [CProp ("sigma",[CProp ("zero",[]); CVar 8]); 
  CProp
  ("quotient",
   [CProp ("times",[CVar 8; CProp ("add1",[CVar 8])]); CProp ("two",[])])]));
add (CProp
("equal",
 [CProp ("plus",[CVar 23; CProp ("add1",[CVar 24])]); 
  CProp
  ("if",
   [CProp ("numberp",[CVar 24]); 
    CProp ("add1",[CProp ("plus",[CVar 23; CVar 24])]); 
    CProp ("add1",[CVar 23])])]));
add (CProp
("equal",
 [CProp
  ("equal",
   [CProp ("difference",[CVar 23; CVar 24]); 
    CProp ("difference",[CVar 25; CVar 24])]); 
  CProp
  ("if",
   [CProp ("lt",[CVar 23; CVar 24]); 
    CProp ("not",[CProp ("lt",[CVar 24; CVar 25])]); 
    CProp
    ("if",
     [CProp ("lt",[CVar 25; CVar 24]); 
      CProp ("not",[CProp ("lt",[CVar 24; CVar 23])]); 
      CProp ("equal",[CProp ("fix",[CVar 23]); CProp ("fix",[CVar 25])])])])])
);
add (CProp
("equal",
 [CProp
  ("meaning",
   [CProp ("plus_tree",[CProp ("delete",[CVar 23; CVar 24])]); CVar 0]); 
  CProp
  ("if",
   [CProp ("member",[CVar 23; CVar 24]); 
    CProp
    ("difference",
     [CProp ("meaning",[CProp ("plus_tree",[CVar 24]); CVar 0]); 
      CProp ("meaning",[CVar 23; CVar 0])]); 
    CProp ("meaning",[CProp ("plus_tree",[CVar 24]); CVar 0])])]));
add (CProp
("equal",
 [CProp ("times",[CVar 23; CProp ("add1",[CVar 24])]); 
  CProp
  ("if",
   [CProp ("numberp",[CVar 24]); 
    CProp
    ("plus",
     [CVar 23; CProp ("times",[CVar 23; CVar 24]); 
      CProp ("fix",[CVar 23])])])]));
add (CProp
("equal",
 [CProp ("nth",[CProp ("nil",[]); CVar 8]); 
  CProp
  ("if",[CProp ("zerop",[CVar 8]); CProp ("nil",[]); CProp ("zero",[])])]));
add (CProp
("equal",
 [CProp ("last",[CProp ("append",[CVar 0; CVar 1])]); 
  CProp
  ("if",
   [CProp ("listp",[CVar 1]); CProp ("last",[CVar 1]); 
    CProp
    ("if",
     [CProp ("listp",[CVar 0]); 
      CProp ("cons",[CProp ("car",[CProp ("last",[CVar 0])]); CVar 1]); 
      CVar 1])])]));
add (CProp
("equal",
 [CProp ("equal",[CProp ("lt",[CVar 23; CVar 24]); CVar 25]); 
  CProp
  ("if",
   [CProp ("lt",[CVar 23; CVar 24]); 
    CProp ("equal",[CProp ("true",[]); CVar 25]); 
    CProp ("equal",[CProp ("false",[]); CVar 25])])]));
add (CProp
("equal",
 [CProp ("assignment",[CVar 23; CProp ("append",[CVar 0; CVar 1])]); 
  CProp
  ("if",
   [CProp ("assignedp",[CVar 23; CVar 0]); 
    CProp ("assignment",[CVar 23; CVar 0]); 
    CProp ("assignment",[CVar 23; CVar 1])])]));
add (CProp
("equal",
 [CProp ("car",[CProp ("gother",[CVar 23])]); 
  CProp
  ("if",
   [CProp ("listp",[CVar 23]); 
    CProp ("car",[CProp ("flatten",[CVar 23])]); CProp ("zero",[])])]));
add (CProp
("equal",
 [CProp ("flatten",[CProp ("cdr",[CProp ("gother",[CVar 23])])]); 
  CProp
  ("if",
   [CProp ("listp",[CVar 23]); 
    CProp ("cdr",[CProp ("flatten",[CVar 23])]); 
    CProp ("cons",[CProp ("zero",[]); CProp ("nil",[])])])]));
add (CProp
("equal",
 [CProp ("quotient",[CProp ("times",[CVar 24; CVar 23]); CVar 24]); 
  CProp
  ("if",
   [CProp ("zerop",[CVar 24]); CProp ("zero",[]); 
    CProp ("fix",[CVar 23])])]));
add (CProp
("equal",
 [CProp ("get",[CVar 9; CProp ("set",[CVar 8; CVar 21; CVar 12])]); 
  CProp
  ("if",
   [CProp ("eqp",[CVar 9; CVar 8]); CVar 21; 
    CProp ("get",[CVar 9; CVar 12])])]))

(* Tautology checker *)

let truep (x, lst) =
  match x with
    Prop(head, _) ->
      head.name = "true" or List.mem x lst
  | _ ->
      List.mem x lst

and falsep (x, lst) =
  match x with
    Prop(head, _) ->
      head.name = "false" or List.mem x lst
  | _ ->
      List.mem x lst


let rec tautologyp (x, true_lst, false_lst) =
 if truep (x, true_lst) then true else
 if falsep (x, false_lst) then false else begin
(*
 print_term x; print_newline();
*)
 match x with
     Var _ -> false
   | Prop (head,[test; yes; no]) as p ->
        if head.name = "if" then
          if truep (test, true_lst) then
            tautologyp (yes, true_lst, false_lst)
          else if falsep (test, false_lst) then
            tautologyp (no, true_lst, false_lst)
          else tautologyp (yes, test::true_lst, false_lst) &
               tautologyp (no, true_lst, test::false_lst)
        else
          false
  end


let tautp x = 
(*  print_term x; print_string"\n"; *)
  let y = rewrite x in
(*    print_term y; print_string "\n"; *)
    tautologyp (y, [], [])

(* the benchmark *)

let subst =
[Bind(23, cterm_to_term(
             CProp
              ("f",
               [CProp
                ("plus",
                 [CProp ("plus",[CVar 0; CVar 1]);
                  CProp ("plus",[CVar 2; CProp ("zero",[])])])])));
 Bind(24, cterm_to_term(
             CProp
              ("f",
               [CProp
                ("times",
                 [CProp ("times",[CVar 0; CVar 1]);
                  CProp ("plus",[CVar 2; CVar 3])])])));
 Bind(25, cterm_to_term(
             CProp
              ("f",
               [CProp
                ("reverse",
                 [CProp
                  ("append",
                   [CProp ("append",[CVar 0; CVar 1]);
                    CProp ("nil",[])])])])));
 Bind(20, cterm_to_term(
             CProp
              ("equal",
               [CProp ("plus",[CVar 0; CVar 1]);
                CProp ("difference",[CVar 23; CVar 24])])));
 Bind(22, cterm_to_term(
             CProp
              ("lt",
               [CProp ("remainder",[CVar 0; CVar 1]);
                CProp ("member",[CVar 0; CProp ("length",[CVar 1])])])))]

let term = cterm_to_term(
           CProp
            ("implies",
             [CProp
              ("and",
               [CProp ("implies",[CVar 23; CVar 24]);
                CProp
                ("and",
                 [CProp ("implies",[CVar 24; CVar 25]);
                  CProp
                  ("and",
                   [CProp ("implies",[CVar 25; CVar 20]);
                    CProp ("implies",[CVar 20; CVar 22])])])]);
              CProp ("implies",[CVar 23; CVar 22])]))

let _ =
  if tautp (apply_subst subst term) then
    print_string "Proved!\n"
  else
    print_string "Cannot prove!\n";
  exit 0

(*********
with
    failure s ->
      print_string "Exception failure("; print_string s; print_string ")\n"
  | Unify ->
      print_string "Exception Unify\n"
  | match_failure(file,start,stop) ->
      print_string "Exception match_failure(";
      print_string file;
      print_string ",";
      print_int start;
      print_string ",";
      print_int stop;
      print_string ")\n"
  | _ ->
      print_string "Exception ?\n"

**********)