# File int_arith1.ML

    (*  Title:      HOL/Integ/int_arith1.ML
        ID:         $Id: int_arith1.ML,v 1.42 2005/08/01 17:20:26 wenzelm Exp $
        Authors:    Larry Paulson and Tobias Nipkow

    Simprocs and decision procedure for linear arithmetic.
    *)

    (** Misc ML bindings **)

    val bin_succ_Pls = thm"bin_succ_Pls";
    val bin_succ_Min = thm"bin_succ_Min";
    val bin_succ_1 = thm"bin_succ_1";
    val bin_succ_0 = thm"bin_succ_0";

    val bin_pred_Pls = thm"bin_pred_Pls";
    val bin_pred_Min = thm"bin_pred_Min";
    val bin_pred_1 = thm"bin_pred_1";
    val bin_pred_0 = thm"bin_pred_0";

    val bin_minus_Pls = thm"bin_minus_Pls";
    val bin_minus_Min = thm"bin_minus_Min";
    val bin_minus_1 = thm"bin_minus_1";
    val bin_minus_0 = thm"bin_minus_0";

    val bin_add_Pls = thm"bin_add_Pls";
    val bin_add_Min = thm"bin_add_Min";
    val bin_add_BIT_11 = thm"bin_add_BIT_11";
    val bin_add_BIT_10 = thm"bin_add_BIT_10";
    val bin_add_BIT_0 = thm"bin_add_BIT_0";
    val bin_add_Pls_right = thm"bin_add_Pls_right";
    val bin_add_Min_right = thm"bin_add_Min_right";

    val bin_mult_Pls = thm"bin_mult_Pls";
    val bin_mult_Min = thm"bin_mult_Min";
    val bin_mult_1 = thm"bin_mult_1";
    val bin_mult_0 = thm"bin_mult_0";

    val neg_def = thm "neg_def";
    val iszero_def = thm "iszero_def";

    val number_of_succ = thm"number_of_succ";
    val number_of_pred = thm"number_of_pred";
    val number_of_minus = thm"number_of_minus";
    val number_of_add = thm"number_of_add";
    val diff_number_of_eq = thm"diff_number_of_eq";
    val number_of_mult = thm"number_of_mult";
    val double_number_of_BIT = thm"double_number_of_BIT";
    val numeral_0_eq_0 = thm"numeral_0_eq_0";
    val numeral_1_eq_1 = thm"numeral_1_eq_1";
    val numeral_m1_eq_minus_1 = thm"numeral_m1_eq_minus_1";
    val mult_minus1 = thm"mult_minus1";
    val mult_minus1_right = thm"mult_minus1_right";
    val minus_number_of_mult = thm"minus_number_of_mult";
    val zero_less_nat_eq = thm"zero_less_nat_eq";
    val eq_number_of_eq = thm"eq_number_of_eq";
    val iszero_number_of_Pls = thm"iszero_number_of_Pls";
    val nonzero_number_of_Min = thm"nonzero_number_of_Min";
    val iszero_number_of_BIT = thm"iszero_number_of_BIT";
    val iszero_number_of_0 = thm"iszero_number_of_0";
    val iszero_number_of_1 = thm"iszero_number_of_1";
    val less_number_of_eq_neg = thm"less_number_of_eq_neg";
    val le_number_of_eq = thm"le_number_of_eq";
    val not_neg_number_of_Pls = thm"not_neg_number_of_Pls";
    val neg_number_of_Min = thm"neg_number_of_Min";
    val neg_number_of_BIT = thm"neg_number_of_BIT";
    val le_number_of_eq_not_less = thm"le_number_of_eq_not_less";
    val abs_number_of = thm"abs_number_of";
    val number_of_reorient = thm"number_of_reorient";
    val add_number_of_left = thm"add_number_of_left";
    val mult_number_of_left = thm"mult_number_of_left";
    val add_number_of_diff1 = thm"add_number_of_diff1";
    val add_number_of_diff2 = thm"add_number_of_diff2";
    val less_iff_diff_less_0 = thm"less_iff_diff_less_0";
    val eq_iff_diff_eq_0 = thm"eq_iff_diff_eq_0";
    val le_iff_diff_le_0 = thm"le_iff_diff_le_0";

    val bin_arith_extra_simps = thms"bin_arith_extra_simps";
    val bin_arith_simps = thms"bin_arith_simps";
    val bin_rel_simps = thms"bin_rel_simps";

    val zless_imp_add1_zle = thm "zless_imp_add1_zle";

    val combine_common_factor = thm"combine_common_factor";
    val eq_add_iff1 = thm"eq_add_iff1";
    val eq_add_iff2 = thm"eq_add_iff2";
    val less_add_iff1 = thm"less_add_iff1";
    val less_add_iff2 = thm"less_add_iff2";
    val le_add_iff1 = thm"le_add_iff1";
    val le_add_iff2 = thm"le_add_iff2";

    val arith_special = thms"arith_special";

    structure Bin_Simprocs =
      struct
      fun prove_conv tacs sg (hyps: thm list) xs (t, u) =
        if t aconv u then NONE
        else
          let val eq = HOLogic.mk_Trueprop (HOLogic.mk_eq (t, u))
          in SOME (Tactic.prove sg xs [] eq (K (EVERY tacs))) end

      fun prove_conv_nohyps tacs sg = prove_conv tacs sg [];
      fun prove_conv_nohyps_novars tacs sg = prove_conv tacs sg [] [];

      fun prep_simproc (name, pats, proc) =
        Simplifier.simproc (Theory.sign_of (the_context())) name pats proc;

      fun is_numeral (Const("Numeral.number_of", _) $ w) = true
        | is_numeral _ = false

      fun simplify_meta_eq f_number_of_eq f_eq =
          mk_meta_eq ([f_eq, f_number_of_eq] MRS trans)

      (*reorientation simprules using ==, for the following simproc*)
      val meta_zero_reorient = zero_reorient RS eq_reflection
      val meta_one_reorient = one_reorient RS eq_reflection
      val meta_number_of_reorient = number_of_reorient RS eq_reflection

      (*reorientation simplification procedure: reorients (polymorphic)
        0 = x, 1 = x, nnn = x provided x isn't 0, 1 or a numeral.*)
      fun reorient_proc sg _ (_ $ t $ u) =
        case u of
    	Const("0", _) => NONE
          | Const("1", _) => NONE
          | Const("Numeral.number_of", _) $ _ => NONE
          | _ => SOME (case t of
    		  Const("0", _) => meta_zero_reorient
    		| Const("1", _) => meta_one_reorient
    		| Const("Numeral.number_of", _) $ _ => meta_number_of_reorient)

      val reorient_simproc =
          prep_simproc ("reorient_simproc", ["0=x", "1=x", "number_of w = x"], reorient_proc)

      end;

    Addsimps arith_special;
    Addsimprocs [Bin_Simprocs.reorient_simproc];

    structure Int_Numeral_Simprocs =
    struct

    (*Maps 0 to Numeral0 and 1 to Numeral1 so that arithmetic in simprocs
      isn't complicated by the abstract 0 and 1.*)
    val numeral_syms = [numeral_0_eq_0 RS sym, numeral_1_eq_1 RS sym];

    (** New term ordering so that AC-rewriting brings numerals to the front **)

    (*Order integers by absolute value and then by sign. The standard integer
      ordering is not well-founded.*)
    fun num_ord (i,j) =
          (case IntInf.compare (IntInf.abs i, IntInf.abs j) of
                EQUAL => int_ord (IntInf.sign i, IntInf.sign j)
              | ord => ord);

    (*This resembles Term.term_ord, but it puts binary numerals before other
      non-atomic terms.*)
    local open Term
    in
    fun numterm_ord (Abs (_, T, t), Abs(_, U, u)) =
          (case numterm_ord (t, u) of EQUAL => typ_ord (T, U) | ord => ord)
      | numterm_ord
         (Const("Numeral.number_of", _) $ v, Const("Numeral.number_of", _) $ w) =
         num_ord (HOLogic.dest_binum v, HOLogic.dest_binum w)
      | numterm_ord (Const("Numeral.number_of", _) $ _, _) = LESS
      | numterm_ord (_, Const("Numeral.number_of", _) $ _) = GREATER
      | numterm_ord (t, u) =
          (case int_ord (size_of_term t, size_of_term u) of
            EQUAL =>
              let val (f, ts) = strip_comb t and (g, us) = strip_comb u in
                (case hd_ord (f, g) of EQUAL => numterms_ord (ts, us) | ord => ord)
              end
          | ord => ord)
    and numterms_ord (ts, us) = list_ord numterm_ord (ts, us)
    end;

    fun numtermless tu = (numterm_ord tu = LESS);

    (*Defined in this file, but perhaps needed only for simprocs of type nat.*)
    val num_ss = HOL_ss settermless numtermless;

    (** Utilities **)

    fun mk_numeral T n = HOLogic.number_of_const T $ HOLogic.mk_bin n;

    (*Decodes a binary INTEGER*)
    fun dest_numeral (Const("0", _)) = 0
      | dest_numeral (Const("1", _)) = 1
      | dest_numeral (Const("Numeral.number_of", _) $ w) =
         (HOLogic.dest_binum w
          handle TERM _ => raise TERM("Int_Numeral_Simprocs.dest_numeral:1", [w]))
      | dest_numeral t = raise TERM("Int_Numeral_Simprocs.dest_numeral:2", [t]);

    fun find_first_numeral past (t::terms) =
            ((dest_numeral t, rev past @ terms)
             handle TERM _ => find_first_numeral (t::past) terms)
      | find_first_numeral past [] = raise TERM("find_first_numeral", []);

    val mk_plus = HOLogic.mk_binop "op +";

    fun mk_minus t =
      let val T = Term.fastype_of t
      in Const ("uminus", T --> T) $ t
      end;

    (*Thus mk_sum[t] yields t+0; longer sums don't have a trailing zero*)
    fun mk_sum T []        = mk_numeral T 0
      | mk_sum T [t,u]     = mk_plus (t, u)
      | mk_sum T (t :: ts) = mk_plus (t, mk_sum T ts);

    (*this version ALWAYS includes a trailing zero*)
    fun long_mk_sum T []        = mk_numeral T 0
      | long_mk_sum T (t :: ts) = mk_plus (t, mk_sum T ts);

    val dest_plus = HOLogic.dest_bin "op +" Term.dummyT;

    (*decompose additions AND subtractions as a sum*)
    fun dest_summing (pos, Const ("op +", _) $ t $ u, ts) =
            dest_summing (pos, t, dest_summing (pos, u, ts))
      | dest_summing (pos, Const ("op -", _) $ t $ u, ts) =
            dest_summing (pos, t, dest_summing (not pos, u, ts))
      | dest_summing (pos, t, ts) =
            if pos then t::ts else mk_minus t :: ts;

    fun dest_sum t = dest_summing (true, t, []);

    val mk_diff = HOLogic.mk_binop "op -";
    val dest_diff = HOLogic.dest_bin "op -" Term.dummyT;

    val mk_times = HOLogic.mk_binop "op *";

    fun mk_prod T =
      let val one = mk_numeral T 1
      fun mk [] = one
        | mk [t] = t
        | mk (t :: ts) = if t = one then mk ts else mk_times (t, mk ts)
      in mk end;

    (*This version ALWAYS includes a trailing one*)
    fun long_mk_prod T []        = mk_numeral T 1
      | long_mk_prod T (t :: ts) = mk_times (t, mk_prod T ts);

    val dest_times = HOLogic.dest_bin "op *" Term.dummyT;

    fun dest_prod t =
          let val (t,u) = dest_times t
          in  dest_prod t @ dest_prod u  end
          handle TERM _ => [t];

    (*DON'T do the obvious simplifications; that would create special cases*)
    fun mk_coeff (k, t) = mk_times (mk_numeral (Term.fastype_of t) k, t);

    (*Express t as a product of (possibly) a numeral with other sorted terms*)
    fun dest_coeff sign (Const ("uminus", _) $ t) = dest_coeff (~sign) t
      | dest_coeff sign t =
        let val ts = sort Term.term_ord (dest_prod t)
            val (n, ts') = find_first_numeral [] ts
                              handle TERM _ => (1, ts)
        in (sign*n, mk_prod (Term.fastype_of t) ts') end;

    (*Find first coefficient-term THAT MATCHES u*)
    fun find_first_coeff past u [] = raise TERM("find_first_coeff", [])
      | find_first_coeff past u (t::terms) =
            let val (n,u') = dest_coeff 1 t
            in  if u aconv u' then (n, rev past @ terms)
                              else find_first_coeff (t::past) u terms
            end
            handle TERM _ => find_first_coeff (t::past) u terms;

    (*Simplify Numeral0+n, n+Numeral0, Numeral1*n, n*Numeral1*)
    val add_0s =  thms "add_0s";
    val mult_1s = thms "mult_1s";

    (*To perform binary arithmetic.  The "left" rewriting handles patterns
      created by the simprocs, such as 3 * (5 * x). *)
    val bin_simps = [numeral_0_eq_0 RS sym, numeral_1_eq_1 RS sym,
                     add_number_of_left, mult_number_of_left] @
                    bin_arith_simps @ bin_rel_simps;

    (*Binary arithmetic BUT NOT ADDITION since it may collapse adjacent terms
      during re-arrangement*)
    val non_add_bin_simps =
        bin_simps \\ [add_number_of_left, number_of_add RS sym];

    (*To evaluate binary negations of coefficients*)
    val minus_simps = [numeral_m1_eq_minus_1 RS sym, number_of_minus RS sym,
                       bin_minus_1, bin_minus_0, bin_minus_Pls, bin_minus_Min,
                       bin_pred_1, bin_pred_0, bin_pred_Pls, bin_pred_Min];

    (*To let us treat subtraction as addition*)
    val diff_simps = [diff_minus, minus_add_distrib, minus_minus];

    (*push the unary minus down: - x * y = x * - y *)
    val minus_mult_eq_1_to_2 =
        [minus_mult_left RS sym, minus_mult_right] MRS trans |> standard;

    (*to extract again any uncancelled minuses*)
    val minus_from_mult_simps =
        [minus_minus, minus_mult_left RS sym, minus_mult_right RS sym];

    (*combine unary minus with numeric literals, however nested within a product*)
    val mult_minus_simps =
        [mult_assoc, minus_mult_left, minus_mult_eq_1_to_2];

    (*Apply the given rewrite (if present) just once*)
    fun trans_tac NONE      = all_tac
      | trans_tac (SOME th) = ALLGOALS (rtac (th RS trans));

    fun simplify_meta_eq rules ss =
        simplify (Simplifier.inherit_bounds ss HOL_basic_ss addeqcongs[eq_cong2] addsimps rules)
        o mk_meta_eq;

    structure CancelNumeralsCommon =
      struct
      val mk_sum            = mk_sum
      val dest_sum          = dest_sum
      val mk_coeff          = mk_coeff
      val dest_coeff        = dest_coeff 1
      val find_first_coeff  = find_first_coeff []
      val trans_tac         = fn _ => trans_tac
      fun norm_tac ss =
        let val num_ss' = Simplifier.inherit_bounds ss num_ss in
          ALLGOALS (simp_tac (num_ss' addsimps numeral_syms @ add_0s @ mult_1s @
                                             diff_simps @ minus_simps @ add_ac))
          THEN ALLGOALS (simp_tac (num_ss' addsimps non_add_bin_simps @ mult_minus_simps))
          THEN ALLGOALS (simp_tac (num_ss' addsimps minus_from_mult_simps @ add_ac @ mult_ac))
        end
      fun numeral_simp_tac ss =
        ALLGOALS (simp_tac (Simplifier.inherit_bounds ss HOL_ss addsimps add_0s @ bin_simps))
      val simplify_meta_eq = simplify_meta_eq (add_0s @ mult_1s)
      end;

    structure EqCancelNumerals = CancelNumeralsFun
     (open CancelNumeralsCommon
      val prove_conv = Bin_Simprocs.prove_conv
      val mk_bal   = HOLogic.mk_eq
      val dest_bal = HOLogic.dest_bin "op =" Term.dummyT
      val bal_add1 = eq_add_iff1 RS trans
      val bal_add2 = eq_add_iff2 RS trans
    );

    structure LessCancelNumerals = CancelNumeralsFun
     (open CancelNumeralsCommon
      val prove_conv = Bin_Simprocs.prove_conv
      val mk_bal   = HOLogic.mk_binrel "op <"
      val dest_bal = HOLogic.dest_bin "op <" Term.dummyT
      val bal_add1 = less_add_iff1 RS trans
      val bal_add2 = less_add_iff2 RS trans
    );

    structure LeCancelNumerals = CancelNumeralsFun
     (open CancelNumeralsCommon
      val prove_conv = Bin_Simprocs.prove_conv
      val mk_bal   = HOLogic.mk_binrel "op <="
      val dest_bal = HOLogic.dest_bin "op <=" Term.dummyT
      val bal_add1 = le_add_iff1 RS trans
      val bal_add2 = le_add_iff2 RS trans
    );

    val cancel_numerals =
      map Bin_Simprocs.prep_simproc
       [("inteq_cancel_numerals",
         ["(l::'a::number_ring) + m = n",
          "(l::'a::number_ring) = m + n",
          "(l::'a::number_ring) - m = n",
          "(l::'a::number_ring) = m - n",
          "(l::'a::number_ring) * m = n",
          "(l::'a::number_ring) = m * n"],
         EqCancelNumerals.proc),
        ("intless_cancel_numerals",
         ["(l::'a::{ordered_idom,number_ring}) + m < n",
          "(l::'a::{ordered_idom,number_ring}) < m + n",
          "(l::'a::{ordered_idom,number_ring}) - m < n",
          "(l::'a::{ordered_idom,number_ring}) < m - n",
          "(l::'a::{ordered_idom,number_ring}) * m < n",
          "(l::'a::{ordered_idom,number_ring}) < m * n"],
         LessCancelNumerals.proc),
        ("intle_cancel_numerals",
         ["(l::'a::{ordered_idom,number_ring}) + m <= n",
          "(l::'a::{ordered_idom,number_ring}) <= m + n",
          "(l::'a::{ordered_idom,number_ring}) - m <= n",
          "(l::'a::{ordered_idom,number_ring}) <= m - n",
          "(l::'a::{ordered_idom,number_ring}) * m <= n",
          "(l::'a::{ordered_idom,number_ring}) <= m * n"],
         LeCancelNumerals.proc)];

    structure CombineNumeralsData =
      struct
      val add               = IntInf.+
      val mk_sum            = long_mk_sum    (*to work for e.g. 2*x + 3*x *)
      val dest_sum          = dest_sum
      val mk_coeff          = mk_coeff
      val dest_coeff        = dest_coeff 1
      val left_distrib      = combine_common_factor RS trans
      val prove_conv        = Bin_Simprocs.prove_conv_nohyps
      val trans_tac         = fn _ => trans_tac
      fun norm_tac ss =
        let val num_ss' = Simplifier.inherit_bounds ss num_ss in
          ALLGOALS (simp_tac (num_ss' addsimps numeral_syms @ add_0s @ mult_1s @
                                              diff_simps @ minus_simps @ add_ac))
          THEN ALLGOALS (simp_tac (num_ss' addsimps non_add_bin_simps @ mult_minus_simps))
          THEN ALLGOALS (simp_tac (num_ss' addsimps minus_from_mult_simps @ add_ac @ mult_ac))
        end
      fun numeral_simp_tac ss =
        ALLGOALS (simp_tac (Simplifier.inherit_bounds ss HOL_ss addsimps add_0s @ bin_simps))
      val simplify_meta_eq = simplify_meta_eq (add_0s @ mult_1s)
      end;

    structure CombineNumerals = CombineNumeralsFun(CombineNumeralsData);

    val combine_numerals =
      Bin_Simprocs.prep_simproc
        ("int_combine_numerals",
         ["(i::'a::number_ring) + j", "(i::'a::number_ring) - j"],
         CombineNumerals.proc);

    end;

    Addsimprocs Int_Numeral_Simprocs.cancel_numerals;
    Addsimprocs [Int_Numeral_Simprocs.combine_numerals];

    (*examples:
    print_depth 22;
    set timing;
    set trace_simp;
    fun test s = (Goal s, by (Simp_tac 1));

    test "l + 2 + 2 + 2 + (l + 2) + (oo + 2) = (uu::int)";

    test "2*u = (u::int)";
    test "(i + j + 12 + (k::int)) - 15 = y";
    test "(i + j + 12 + (k::int)) - 5 = y";

    test "y - b < (b::int)";
    test "y - (3*b + c) < (b::int) - 2*c";

    test "(2*x - (u*v) + y) - v*3*u = (w::int)";
    test "(2*x*u*v + (u*v)*4 + y) - v*u*4 = (w::int)";
    test "(2*x*u*v + (u*v)*4 + y) - v*u = (w::int)";
    test "u*v - (x*u*v + (u*v)*4 + y) = (w::int)";

    test "(i + j + 12 + (k::int)) = u + 15 + y";
    test "(i + j*2 + 12 + (k::int)) = j + 5 + y";

    test "2*y + 3*z + 6*w + 2*y + 3*z + 2*u = 2*y' + 3*z' + 6*w' + 2*y' + 3*z' + u + (vv::int)";

    test "a + -(b+c) + b = (d::int)";
    test "a + -(b+c) - b = (d::int)";

    (*negative numerals*)
    test "(i + j + -2 + (k::int)) - (u + 5 + y) = zz";
    test "(i + j + -3 + (k::int)) < u + 5 + y";
    test "(i + j + 3 + (k::int)) < u + -6 + y";
    test "(i + j + -12 + (k::int)) - 15 = y";
    test "(i + j + 12 + (k::int)) - -15 = y";
    test "(i + j + -12 + (k::int)) - -15 = y";
    *)

    (** Constant folding for multiplication in semirings **)

    (*We do not need folding for addition: combine_numerals does the same thing*)

    structure Semiring_Times_Assoc_Data : ASSOC_FOLD_DATA =
    struct
      val ss                = HOL_ss
      val eq_reflection     = eq_reflection
      val thy_ref = Theory.self_ref (the_context ())
      val add_ac = mult_ac
    end;

    structure Semiring_Times_Assoc = Assoc_Fold (Semiring_Times_Assoc_Data);

    val assoc_fold_simproc =
      Bin_Simprocs.prep_simproc
       ("semiring_assoc_fold", ["(a::'a::comm_semiring_1_cancel) * b"],
        Semiring_Times_Assoc.proc);

    Addsimprocs [assoc_fold_simproc];

    (*** decision procedure for linear arithmetic ***)

    (*---------------------------------------------------------------------------*)
    (* Linear arithmetic                                                         *)
    (*---------------------------------------------------------------------------*)

    (*
    Instantiation of the generic linear arithmetic package for int.
    *)

    (* Update parameters of arithmetic prover *)
    local

    (* reduce contradictory <= to False *)
    val add_rules =
        simp_thms @ bin_arith_simps @ bin_rel_simps @ arith_special @
        [neg_le_iff_le, numeral_0_eq_0, numeral_1_eq_1,
         minus_zero, diff_minus, left_minus, right_minus,
         mult_zero_left, mult_zero_right, mult_1, mult_1_right,
         minus_mult_left RS sym, minus_mult_right RS sym,
         minus_add_distrib, minus_minus, mult_assoc,
         of_nat_0, of_nat_1, of_nat_Suc, of_nat_add, of_nat_mult,
         of_int_0, of_int_1, of_int_add, of_int_mult, int_eq_of_nat];

    val simprocs = [assoc_fold_simproc, Int_Numeral_Simprocs.combine_numerals]@
                   Int_Numeral_Simprocs.cancel_numerals;

    in

    val int_arith_setup =
     [Fast_Arith.map_data (fn {add_mono_thms, mult_mono_thms, inj_thms, lessD, neqE, simpset} =>
       {add_mono_thms = add_mono_thms,
        mult_mono_thms = [mult_strict_left_mono,mult_left_mono] @ mult_mono_thms,
        inj_thms = [zle_int RS iffD2,int_int_eq RS iffD2] @ inj_thms,
        lessD = lessD @ [zless_imp_add1_zle],
        neqE = thm "linorder_neqE_int" :: neqE,
        simpset = simpset addsimps add_rules
                          addsimprocs simprocs
                          addcongs [if_weak_cong]}),
      arith_inj_const ("IntDef.of_nat", HOLogic.natT --> HOLogic.intT),
      arith_inj_const ("IntDef.int", HOLogic.natT --> HOLogic.intT),
      arith_discrete "IntDef.int"];

    end;

    val fast_int_arith_simproc =
      Simplifier.simproc (Theory.sign_of (the_context()))
      "fast_int_arith"
         ["(m::'a::{ordered_idom,number_ring}) < n",
          "(m::'a::{ordered_idom,number_ring}) <= n",
          "(m::'a::{ordered_idom,number_ring}) = n"] Fast_Arith.lin_arith_prover;

    Addsimprocs [fast_int_arith_simproc]

    (* Some test data
    Goal "!!a::int. [| a <= b; c <= d; x+y<z |] ==> a+c <= b+d";
    by (fast_arith_tac 1);
    Goal "!!a::int. [| a < b; c < d |] ==> a-d+ 2 <= b+(-c)";
    by (fast_arith_tac 1);
    Goal "!!a::int. [| a < b; c < d |] ==> a+c+ 1 < b+d";
    by (fast_arith_tac 1);
    Goal "!!a::int. [| a <= b; b+b <= c |] ==> a+a <= c";
    by (fast_arith_tac 1);
    Goal "!!a::int. [| a+b <= i+j; a<=b; i<=j |] \
    \     ==> a+a <= j+j";
    by (fast_arith_tac 1);
    Goal "!!a::int. [| a+b < i+j; a<b; i<j |] \
    \     ==> a+a - - -1 < j+j - 3";
    by (fast_arith_tac 1);
    Goal "!!a::int. a+b+c <= i+j+k & a<=b & b<=c & i<=j & j<=k --> a+a+a <= k+k+k";
    by (arith_tac 1);
    Goal "!!a::int. [| a+b+c+d <= i+j+k+l; a<=b; b<=c; c<=d; i<=j; j<=k; k<=l |] \
    \     ==> a <= l";
    by (fast_arith_tac 1);
    Goal "!!a::int. [| a+b+c+d <= i+j+k+l; a<=b; b<=c; c<=d; i<=j; j<=k; k<=l |] \
    \     ==> a+a+a+a <= l+l+l+l";
    by (fast_arith_tac 1);
    Goal "!!a::int. [| a+b+c+d <= i+j+k+l; a<=b; b<=c; c<=d; i<=j; j<=k; k<=l |] \
    \     ==> a+a+a+a+a <= l+l+l+l+i";
    by (fast_arith_tac 1);
    Goal "!!a::int. [| a+b+c+d <= i+j+k+l; a<=b; b<=c; c<=d; i<=j; j<=k; k<=l |] \
    \     ==> a+a+a+a+a+a <= l+l+l+l+i+l";
    by (fast_arith_tac 1);
    Goal "!!a::int. [| a+b+c+d <= i+j+k+l; a<=b; b<=c; c<=d; i<=j; j<=k; k<=l |] \
    \     ==> 6*a <= 5*l+i";
    by (fast_arith_tac 1);
    *)