src/HOL/Tools/numeral_simprocs.ML

moved Inductive.myinv to Fun.inv; tuned

(* Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
   Copyright   2000  University of Cambridge

Simprocs for the integer numerals.
*)

(*To quote from Provers/Arith/cancel_numeral_factor.ML:

Cancels common coefficients in balanced expressions:

     u*#m ~~ u'*#m'  ==  #n*u ~~ #n'*u'

where ~~ is an appropriate balancing operation (e.g. =, <=, <, div, /)
and d = gcd(m,m') and n=m/d and n'=m'/d.
*)

signature NUMERAL_SIMPROCS =
sig
  val mk_sum: typ -> term list -> term
  val dest_sum: term -> term list

  val assoc_fold_simproc: simproc
  val combine_numerals: simproc
  val cancel_numerals: simproc list
  val cancel_factors: simproc list
  val cancel_numeral_factors: simproc list
  val field_combine_numerals: simproc
  val field_cancel_numeral_factors: simproc list
  val num_ss: simpset
end;

structure Numeral_Simprocs : NUMERAL_SIMPROCS =
struct

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

fun find_first_numeral past (t::terms) =
        ((snd (HOLogic.dest_number 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 @{const_name HOL.plus};

fun mk_minus t = 
  let val T = Term.fastype_of t
  in Const (@{const_name HOL.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_number 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_number T 0
  | long_mk_sum T (t :: ts) = mk_plus (t, mk_sum T ts);

val dest_plus = HOLogic.dest_bin @{const_name HOL.plus} Term.dummyT;

(*decompose additions AND subtractions as a sum*)
fun dest_summing (pos, Const (@{const_name HOL.plus}, _) $ t $ u, ts) =
        dest_summing (pos, t, dest_summing (pos, u, ts))
  | dest_summing (pos, Const (@{const_name HOL.minus}, _) $ 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 @{const_name HOL.minus};
val dest_diff = HOLogic.dest_bin @{const_name HOL.minus} Term.dummyT;

val mk_times = HOLogic.mk_binop @{const_name HOL.times};

fun one_of T = Const(@{const_name HOL.one},T);

(* build product with trailing 1 rather than Numeral 1 in order to avoid the
   unnecessary restriction to type class number_ring
   which is not required for cancellation of common factors in divisions.
*)
fun mk_prod T = 
  let val one = one_of T
  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 []        = one_of T
  | long_mk_prod T (t :: ts) = mk_times (t, mk_prod T ts);

val dest_times = HOLogic.dest_bin @{const_name HOL.times} 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_number (Term.fastype_of t) k, t);

(*Express t as a product of (possibly) a numeral with other sorted terms*)
fun dest_coeff sign (Const (@{const_name HOL.uminus}, _) $ t) = dest_coeff (~sign) t
  | dest_coeff sign t =
    let val ts = sort TermOrd.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;

(*Fractions as pairs of ints. Can't use Rat.rat because the representation
  needs to preserve negative values in the denominator.*)
fun mk_frac (p, q) = if q = 0 then raise Div else (p, q);

(*Don't reduce fractions; sums must be proved by rule add_frac_eq.
  Fractions are reduced later by the cancel_numeral_factor simproc.*)
fun add_frac ((p1, q1), (p2, q2)) = (p1 * q2 + p2 * q1, q1 * q2);

val mk_divide = HOLogic.mk_binop @{const_name HOL.divide};

(*Build term (p / q) * t*)
fun mk_fcoeff ((p, q), t) =
  let val T = Term.fastype_of t
  in mk_times (mk_divide (mk_number T p, mk_number T q), t) end;

(*Express t as a product of a fraction with other sorted terms*)
fun dest_fcoeff sign (Const (@{const_name HOL.uminus}, _) $ t) = dest_fcoeff (~sign) t
  | dest_fcoeff sign (Const (@{const_name HOL.divide}, _) $ t $ u) =
    let val (p, t') = dest_coeff sign t
        val (q, u') = dest_coeff 1 u
    in (mk_frac (p, q), mk_divide (t', u')) end
  | dest_fcoeff sign t =
    let val (p, t') = dest_coeff sign t
        val T = Term.fastype_of t
    in (mk_frac (p, 1), mk_divide (t', one_of T)) end;


(** 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 int_ord (abs i, abs j) of
    EQUAL => int_ord (Int.sign i, Int.sign j) 
  | ord => ord);

(*This resembles TermOrd.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 => TermOrd.typ_ord (T, U) | ord => ord)
  | numterm_ord
     (Const(@{const_name Int.number_of}, _) $ v, Const(@{const_name Int.number_of}, _) $ w) =
     num_ord (HOLogic.dest_numeral v, HOLogic.dest_numeral w)
  | numterm_ord (Const(@{const_name Int.number_of}, _) $ _, _) = LESS
  | numterm_ord (_, Const(@{const_name Int.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 TermOrd.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);

val num_ss = HOL_ss settermless numtermless;

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

(*Simplify Numeral0+n, n+Numeral0, Numeral1*n, n*Numeral1, 1*x, x*1, x/1 *)
val add_0s =  @{thms add_0s};
val mult_1s = @{thms mult_1s mult_1_left mult_1_right divide_1};

(*Simplify inverse Numeral1, a/Numeral1*)
val inverse_1s = [@{thm inverse_numeral_1}];
val divide_1s = [@{thm divide_numeral_1}];

(*To perform binary arithmetic.  The "left" rewriting handles patterns
  created by the Numeral_Simprocs, such as 3 * (5 * x). *)
val simps = [@{thm numeral_0_eq_0} RS sym, @{thm numeral_1_eq_1} RS sym,
                 @{thm add_number_of_left}, @{thm mult_number_of_left}] @
                @{thms arith_simps} @ @{thms rel_simps};

(*Binary arithmetic BUT NOT ADDITION since it may collapse adjacent terms
  during re-arrangement*)
val non_add_simps =
  subtract Thm.eq_thm [@{thm add_number_of_left}, @{thm number_of_add} RS sym] simps;

(*To evaluate binary negations of coefficients*)
val minus_simps = [@{thm numeral_m1_eq_minus_1} RS sym, @{thm number_of_minus} RS sym] @
                   @{thms minus_bin_simps} @ @{thms pred_bin_simps};

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

(*To let us treat division as multiplication*)
val divide_simps = [@{thm divide_inverse}, @{thm inverse_mult_distrib}, @{thm inverse_inverse_eq}];

(*push the unary minus down: - x * y = x * - y *)
val minus_mult_eq_1_to_2 =
    [@{thm mult_minus_left}, @{thm minus_mult_right}] MRS trans |> standard;

(*to extract again any uncancelled minuses*)
val minus_from_mult_simps =
    [@{thm minus_minus}, @{thm mult_minus_left}, @{thm mult_minus_right}];

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

val norm_ss1 = num_ss addsimps numeral_syms @ add_0s @ mult_1s @
  diff_simps @ minus_simps @ @{thms add_ac}
val norm_ss2 = num_ss addsimps non_add_simps @ mult_minus_simps
val norm_ss3 = num_ss addsimps minus_from_mult_simps @ @{thms add_ac} @ @{thms mult_ac}

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 []
  fun trans_tac _       = Arith_Data.trans_tac

  fun norm_tac ss =
    ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss1))
    THEN ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss2))
    THEN ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss3))

  val numeral_simp_ss = HOL_ss addsimps add_0s @ simps
  fun numeral_simp_tac ss = ALLGOALS (simp_tac (Simplifier.inherit_context ss numeral_simp_ss))
  val simplify_meta_eq = Arith_Data.simplify_meta_eq (add_0s @ mult_1s)
  end;


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

structure LessCancelNumerals = CancelNumeralsFun
 (open CancelNumeralsCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binrel @{const_name HOL.less}
  val dest_bal = HOLogic.dest_bin @{const_name HOL.less} Term.dummyT
  val bal_add1 = @{thm less_add_iff1} RS trans
  val bal_add2 = @{thm less_add_iff2} RS trans
);

structure LeCancelNumerals = CancelNumeralsFun
 (open CancelNumeralsCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binrel @{const_name HOL.less_eq}
  val dest_bal = HOLogic.dest_bin @{const_name HOL.less_eq} Term.dummyT
  val bal_add1 = @{thm le_add_iff1} RS trans
  val bal_add2 = @{thm le_add_iff2} RS trans
);

val cancel_numerals =
  map Arith_Data.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"],
     K 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"],
     K 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"],
     K LeCancelNumerals.proc)];

structure CombineNumeralsData =
  struct
  type coeff            = int
  val iszero            = (fn x => x = 0)
  val add               = op +
  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      = @{thm combine_common_factor} RS trans
  val prove_conv        = Arith_Data.prove_conv_nohyps
  fun trans_tac _       = Arith_Data.trans_tac

  fun norm_tac ss =
    ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss1))
    THEN ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss2))
    THEN ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss3))

  val numeral_simp_ss = HOL_ss addsimps add_0s @ simps
  fun numeral_simp_tac ss = ALLGOALS (simp_tac (Simplifier.inherit_context ss numeral_simp_ss))
  val simplify_meta_eq = Arith_Data.simplify_meta_eq (add_0s @ mult_1s)
  end;

structure CombineNumerals = CombineNumeralsFun(CombineNumeralsData);

(*Version for fields, where coefficients can be fractions*)
structure FieldCombineNumeralsData =
  struct
  type coeff            = int * int
  val iszero            = (fn (p, q) => p = 0)
  val add               = add_frac
  val mk_sum            = long_mk_sum
  val dest_sum          = dest_sum
  val mk_coeff          = mk_fcoeff
  val dest_coeff        = dest_fcoeff 1
  val left_distrib      = @{thm combine_common_factor} RS trans
  val prove_conv        = Arith_Data.prove_conv_nohyps
  fun trans_tac _       = Arith_Data.trans_tac

  val norm_ss1a = norm_ss1 addsimps inverse_1s @ divide_simps
  fun norm_tac ss =
    ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss1a))
    THEN ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss2))
    THEN ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss3))

  val numeral_simp_ss = HOL_ss addsimps add_0s @ simps @ [@{thm add_frac_eq}]
  fun numeral_simp_tac ss = ALLGOALS (simp_tac (Simplifier.inherit_context ss numeral_simp_ss))
  val simplify_meta_eq = Arith_Data.simplify_meta_eq (add_0s @ mult_1s @ divide_1s)
  end;

structure FieldCombineNumerals = CombineNumeralsFun(FieldCombineNumeralsData);

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

val field_combine_numerals =
  Arith_Data.prep_simproc
    ("field_combine_numerals", 
     ["(i::'a::{number_ring,field,division_by_zero}) + j",
      "(i::'a::{number_ring,field,division_by_zero}) - j"], 
     K FieldCombineNumerals.proc);

(** 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 assoc_ss = HOL_ss addsimps @{thms mult_ac}
  val eq_reflection = eq_reflection
  fun is_numeral (Const(@{const_name Int.number_of}, _) $ _) = true
    | is_numeral _ = false;
end;

structure Semiring_Times_Assoc = Assoc_Fold (Semiring_Times_Assoc_Data);

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

structure CancelNumeralFactorCommon =
  struct
  val mk_coeff          = mk_coeff
  val dest_coeff        = dest_coeff 1
  fun trans_tac _       = Arith_Data.trans_tac

  val norm_ss1 = HOL_ss addsimps minus_from_mult_simps @ mult_1s
  val norm_ss2 = HOL_ss addsimps simps @ mult_minus_simps
  val norm_ss3 = HOL_ss addsimps @{thms mult_ac}
  fun norm_tac ss =
    ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss1))
    THEN ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss2))
    THEN ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss3))

  val numeral_simp_ss = HOL_ss addsimps
    [@{thm eq_number_of_eq}, @{thm less_number_of}, @{thm le_number_of}] @ simps
  fun numeral_simp_tac ss = ALLGOALS (simp_tac (Simplifier.inherit_context ss numeral_simp_ss))
  val simplify_meta_eq = Arith_Data.simplify_meta_eq
    [@{thm add_0}, @{thm add_0_right}, @{thm mult_zero_left},
      @{thm mult_zero_right}, @{thm mult_Bit1}, @{thm mult_1_right}];
  end

(*Version for semiring_div*)
structure DivCancelNumeralFactor = CancelNumeralFactorFun
 (open CancelNumeralFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binop @{const_name Divides.div}
  val dest_bal = HOLogic.dest_bin @{const_name Divides.div} Term.dummyT
  val cancel = @{thm div_mult_mult1} RS trans
  val neg_exchanges = false
)

(*Version for fields*)
structure DivideCancelNumeralFactor = CancelNumeralFactorFun
 (open CancelNumeralFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binop @{const_name HOL.divide}
  val dest_bal = HOLogic.dest_bin @{const_name HOL.divide} Term.dummyT
  val cancel = @{thm mult_divide_mult_cancel_left} RS trans
  val neg_exchanges = false
)

structure EqCancelNumeralFactor = CancelNumeralFactorFun
 (open CancelNumeralFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_eq
  val dest_bal = HOLogic.dest_bin "op =" Term.dummyT
  val cancel = @{thm mult_cancel_left} RS trans
  val neg_exchanges = false
)

structure LessCancelNumeralFactor = CancelNumeralFactorFun
 (open CancelNumeralFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binrel @{const_name HOL.less}
  val dest_bal = HOLogic.dest_bin @{const_name HOL.less} Term.dummyT
  val cancel = @{thm mult_less_cancel_left} RS trans
  val neg_exchanges = true
)

structure LeCancelNumeralFactor = CancelNumeralFactorFun
 (open CancelNumeralFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binrel @{const_name HOL.less_eq}
  val dest_bal = HOLogic.dest_bin @{const_name HOL.less_eq} Term.dummyT
  val cancel = @{thm mult_le_cancel_left} RS trans
  val neg_exchanges = true
)

val cancel_numeral_factors =
  map Arith_Data.prep_simproc
   [("ring_eq_cancel_numeral_factor",
     ["(l::'a::{idom,number_ring}) * m = n",
      "(l::'a::{idom,number_ring}) = m * n"],
     K EqCancelNumeralFactor.proc),
    ("ring_less_cancel_numeral_factor",
     ["(l::'a::{ordered_idom,number_ring}) * m < n",
      "(l::'a::{ordered_idom,number_ring}) < m * n"],
     K LessCancelNumeralFactor.proc),
    ("ring_le_cancel_numeral_factor",
     ["(l::'a::{ordered_idom,number_ring}) * m <= n",
      "(l::'a::{ordered_idom,number_ring}) <= m * n"],
     K LeCancelNumeralFactor.proc),
    ("int_div_cancel_numeral_factors",
     ["((l::'a::{semiring_div,number_ring}) * m) div n",
      "(l::'a::{semiring_div,number_ring}) div (m * n)"],
     K DivCancelNumeralFactor.proc),
    ("divide_cancel_numeral_factor",
     ["((l::'a::{division_by_zero,field,number_ring}) * m) / n",
      "(l::'a::{division_by_zero,field,number_ring}) / (m * n)",
      "((number_of v)::'a::{division_by_zero,field,number_ring}) / (number_of w)"],
     K DivideCancelNumeralFactor.proc)];

val field_cancel_numeral_factors =
  map Arith_Data.prep_simproc
   [("field_eq_cancel_numeral_factor",
     ["(l::'a::{field,number_ring}) * m = n",
      "(l::'a::{field,number_ring}) = m * n"],
     K EqCancelNumeralFactor.proc),
    ("field_cancel_numeral_factor",
     ["((l::'a::{division_by_zero,field,number_ring}) * m) / n",
      "(l::'a::{division_by_zero,field,number_ring}) / (m * n)",
      "((number_of v)::'a::{division_by_zero,field,number_ring}) / (number_of w)"],
     K DivideCancelNumeralFactor.proc)]


(** Declarations for ExtractCommonTerm **)

(*Find first term that matches u*)
fun find_first_t past u []         = raise TERM ("find_first_t", [])
  | find_first_t past u (t::terms) =
        if u aconv t then (rev past @ terms)
        else find_first_t (t::past) u terms
        handle TERM _ => find_first_t (t::past) u terms;

(** Final simplification for the CancelFactor simprocs **)
val simplify_one = Arith_Data.simplify_meta_eq  
  [@{thm mult_1_left}, @{thm mult_1_right}, @{thm div_by_1}, @{thm numeral_1_eq_1}];

fun cancel_simplify_meta_eq ss cancel_th th =
    simplify_one ss (([th, cancel_th]) MRS trans);

local
  val Tp_Eq = Thm.reflexive (Thm.cterm_of @{theory HOL} HOLogic.Trueprop)
  fun Eq_True_elim Eq = 
    Thm.equal_elim (Thm.combination Tp_Eq (Thm.symmetric Eq)) @{thm TrueI}
in
fun sign_conv pos_th neg_th ss t =
  let val T = fastype_of t;
      val zero = Const(@{const_name HOL.zero}, T);
      val less = Const(@{const_name HOL.less}, [T,T] ---> HOLogic.boolT);
      val pos = less $ zero $ t and neg = less $ t $ zero
      fun prove p =
        Option.map Eq_True_elim (Lin_Arith.simproc ss p)
        handle THM _ => NONE
    in case prove pos of
         SOME th => SOME(th RS pos_th)
       | NONE => (case prove neg of
                    SOME th => SOME(th RS neg_th)
                  | NONE => NONE)
    end;
end

structure CancelFactorCommon =
  struct
  val mk_sum            = long_mk_prod
  val dest_sum          = dest_prod
  val mk_coeff          = mk_coeff
  val dest_coeff        = dest_coeff
  val find_first        = find_first_t []
  fun trans_tac _       = Arith_Data.trans_tac
  val norm_ss = HOL_ss addsimps mult_1s @ @{thms mult_ac}
  fun norm_tac ss = ALLGOALS (simp_tac (Simplifier.inherit_context ss norm_ss))
  val simplify_meta_eq  = cancel_simplify_meta_eq 
  end;

(*mult_cancel_left requires a ring with no zero divisors.*)
structure EqCancelFactor = ExtractCommonTermFun
 (open CancelFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_eq
  val dest_bal = HOLogic.dest_bin "op =" Term.dummyT
  fun simp_conv _ _ = SOME @{thm mult_cancel_left}
);

(*for ordered rings*)
structure LeCancelFactor = ExtractCommonTermFun
 (open CancelFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binrel @{const_name HOL.less_eq}
  val dest_bal = HOLogic.dest_bin @{const_name HOL.less_eq} Term.dummyT
  val simp_conv = sign_conv
    @{thm mult_le_cancel_left_pos} @{thm mult_le_cancel_left_neg}
);

(*for ordered rings*)
structure LessCancelFactor = ExtractCommonTermFun
 (open CancelFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binrel @{const_name HOL.less}
  val dest_bal = HOLogic.dest_bin @{const_name HOL.less} Term.dummyT
  val simp_conv = sign_conv
    @{thm mult_less_cancel_left_pos} @{thm mult_less_cancel_left_neg}
);

(*for semirings with division*)
structure DivCancelFactor = ExtractCommonTermFun
 (open CancelFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binop @{const_name Divides.div}
  val dest_bal = HOLogic.dest_bin @{const_name Divides.div} Term.dummyT
  fun simp_conv _ _ = SOME @{thm div_mult_mult1_if}
);

structure ModCancelFactor = ExtractCommonTermFun
 (open CancelFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binop @{const_name Divides.mod}
  val dest_bal = HOLogic.dest_bin @{const_name Divides.mod} Term.dummyT
  fun simp_conv _ _ = SOME @{thm mod_mult_mult1}
);

(*for idoms*)
structure DvdCancelFactor = ExtractCommonTermFun
 (open CancelFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binrel @{const_name Ring_and_Field.dvd}
  val dest_bal = HOLogic.dest_bin @{const_name Ring_and_Field.dvd} Term.dummyT
  fun simp_conv _ _ = SOME @{thm dvd_mult_cancel_left}
);

(*Version for all fields, including unordered ones (type complex).*)
structure DivideCancelFactor = ExtractCommonTermFun
 (open CancelFactorCommon
  val prove_conv = Arith_Data.prove_conv
  val mk_bal   = HOLogic.mk_binop @{const_name HOL.divide}
  val dest_bal = HOLogic.dest_bin @{const_name HOL.divide} Term.dummyT
  fun simp_conv _ _ = SOME @{thm mult_divide_mult_cancel_left_if}
);

val cancel_factors =
  map Arith_Data.prep_simproc
   [("ring_eq_cancel_factor",
     ["(l::'a::idom) * m = n",
      "(l::'a::idom) = m * n"],
     K EqCancelFactor.proc),
    ("ordered_ring_le_cancel_factor",
     ["(l::'a::ordered_ring) * m <= n",
      "(l::'a::ordered_ring) <= m * n"],
     K LeCancelFactor.proc),
    ("ordered_ring_less_cancel_factor",
     ["(l::'a::ordered_ring) * m < n",
      "(l::'a::ordered_ring) < m * n"],
     K LessCancelFactor.proc),
    ("int_div_cancel_factor",
     ["((l::'a::semiring_div) * m) div n", "(l::'a::semiring_div) div (m * n)"],
     K DivCancelFactor.proc),
    ("int_mod_cancel_factor",
     ["((l::'a::semiring_div) * m) mod n", "(l::'a::semiring_div) mod (m * n)"],
     K ModCancelFactor.proc),
    ("dvd_cancel_factor",
     ["((l::'a::idom) * m) dvd n", "(l::'a::idom) dvd (m * n)"],
     K DvdCancelFactor.proc),
    ("divide_cancel_factor",
     ["((l::'a::{division_by_zero,field}) * m) / n",
      "(l::'a::{division_by_zero,field}) / (m * n)"],
     K DivideCancelFactor.proc)];

end;

Addsimprocs Numeral_Simprocs.cancel_numerals;
Addsimprocs [Numeral_Simprocs.combine_numerals];
Addsimprocs [Numeral_Simprocs.field_combine_numerals];
Addsimprocs [Numeral_Simprocs.assoc_fold_simproc];

(*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";
*)

Addsimprocs Numeral_Simprocs.cancel_numeral_factors;

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

test "9*x = 12 * (y::int)";
test "(9*x) div (12 * (y::int)) = z";
test "9*x < 12 * (y::int)";
test "9*x <= 12 * (y::int)";

test "-99*x = 132 * (y::int)";
test "(-99*x) div (132 * (y::int)) = z";
test "-99*x < 132 * (y::int)";
test "-99*x <= 132 * (y::int)";

test "999*x = -396 * (y::int)";
test "(999*x) div (-396 * (y::int)) = z";
test "999*x < -396 * (y::int)";
test "999*x <= -396 * (y::int)";

test "-99*x = -81 * (y::int)";
test "(-99*x) div (-81 * (y::int)) = z";
test "-99*x <= -81 * (y::int)";
test "-99*x < -81 * (y::int)";

test "-2 * x = -1 * (y::int)";
test "-2 * x = -(y::int)";
test "(-2 * x) div (-1 * (y::int)) = z";
test "-2 * x < -(y::int)";
test "-2 * x <= -1 * (y::int)";
test "-x < -23 * (y::int)";
test "-x <= -23 * (y::int)";
*)

(*And the same examples for fields such as rat or real:
test "0 <= (y::rat) * -2";
test "9*x = 12 * (y::rat)";
test "(9*x) / (12 * (y::rat)) = z";
test "9*x < 12 * (y::rat)";
test "9*x <= 12 * (y::rat)";

test "-99*x = 132 * (y::rat)";
test "(-99*x) / (132 * (y::rat)) = z";
test "-99*x < 132 * (y::rat)";
test "-99*x <= 132 * (y::rat)";

test "999*x = -396 * (y::rat)";
test "(999*x) / (-396 * (y::rat)) = z";
test "999*x < -396 * (y::rat)";
test "999*x <= -396 * (y::rat)";

test  "(- ((2::rat) * x) <= 2 * y)";
test "-99*x = -81 * (y::rat)";
test "(-99*x) / (-81 * (y::rat)) = z";
test "-99*x <= -81 * (y::rat)";
test "-99*x < -81 * (y::rat)";

test "-2 * x = -1 * (y::rat)";
test "-2 * x = -(y::rat)";
test "(-2 * x) / (-1 * (y::rat)) = z";
test "-2 * x < -(y::rat)";
test "-2 * x <= -1 * (y::rat)";
test "-x < -23 * (y::rat)";
test "-x <= -23 * (y::rat)";
*)

Addsimprocs Numeral_Simprocs.cancel_factors;


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

test "x*k = k*(y::int)";
test "k = k*(y::int)";
test "a*(b*c) = (b::int)";
test "a*(b*c) = d*(b::int)*(x*a)";

test "(x*k) div (k*(y::int)) = (uu::int)";
test "(k) div (k*(y::int)) = (uu::int)";
test "(a*(b*c)) div ((b::int)) = (uu::int)";
test "(a*(b*c)) div (d*(b::int)*(x*a)) = (uu::int)";
*)

(*And the same examples for fields such as rat or real:
print_depth 22;
set timing;
set trace_simp;
fun test s = (Goal s; by (Asm_simp_tac 1));

test "x*k = k*(y::rat)";
test "k = k*(y::rat)";
test "a*(b*c) = (b::rat)";
test "a*(b*c) = d*(b::rat)*(x*a)";


test "(x*k) / (k*(y::rat)) = (uu::rat)";
test "(k) / (k*(y::rat)) = (uu::rat)";
test "(a*(b*c)) / ((b::rat)) = (uu::rat)";
test "(a*(b*c)) / (d*(b::rat)*(x*a)) = (uu::rat)";

(*FIXME: what do we do about this?*)
test "a*(b*c)/(y*z) = d*(b::rat)*(x*a)/z";
*)