src/HOL/Integ/NatSimprocs.ML

proper close_locale;

(*  Title:      HOL/NatSimprocs.ML
    ID:         $Id$
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   2000  University of Cambridge

Simprocs for nat numerals (see also nat_simprocs.ML).
*)

(** For simplifying  Suc m - #n **)

Goal "Numeral0 < n ==> Suc m - n = m - (n - Numeral1)";
by (asm_simp_tac (simpset() addsimps [numeral_0_eq_0, numeral_1_eq_1]
			    addsplits [nat_diff_split]) 1);
qed "Suc_diff_eq_diff_pred";

(*Now just instantiating n to (number_of v) does the right simplification,
  but with some redundant inequality tests.*)
Goal "neg (number_of (bin_pred v)) = (number_of v = (0::nat))";
by (subgoal_tac "neg (number_of (bin_pred v)) = (number_of v < Suc 0)" 1);
by (asm_simp_tac (HOL_ss addsimps [less_Suc_eq_le, le_0_eq]) 1); 
by (stac less_number_of_Suc 1);
by (Simp_tac 1);
qed "neg_number_of_bin_pred_iff_0";

Goal "neg (number_of (bin_minus v)) ==> \
\     Suc m - (number_of v) = m - (number_of (bin_pred v))";
by (stac Suc_diff_eq_diff_pred 1);
by (Simp_tac 1);
by (Simp_tac 1);
by (asm_full_simp_tac
    (simpset_of Int.thy addsimps [diff_nat_number_of, less_0_number_of RS sym,
                                  neg_number_of_bin_pred_iff_0]) 1);
qed "Suc_diff_number_of";

(* now redundant because of the inverse_fold simproc
    Addsimps [Suc_diff_number_of]; *)

Goal "nat_case a f (number_of v) = \
\       (let pv = number_of (bin_pred v) in \
\        if neg pv then a else f (nat pv))";
by (simp_tac
    (simpset() addsplits [nat.split]
                        addsimps [Let_def, neg_number_of_bin_pred_iff_0]) 1);
qed "nat_case_number_of";

Goal "nat_case a f ((number_of v) + n) = \
\      (let pv = number_of (bin_pred v) in \
\        if neg pv then nat_case a f n else f (nat pv + n))";
by (stac add_eq_if 1);
by (asm_simp_tac
    (simpset() addsplits [nat.split]
               addsimps [numeral_1_eq_Suc_0 RS sym, Let_def, 
                   neg_imp_number_of_eq_0, neg_number_of_bin_pred_iff_0]) 1);
qed "nat_case_add_eq_if";

Addsimps [nat_case_number_of, nat_case_add_eq_if];


Goal "nat_rec a f (number_of v) = \
\       (let pv = number_of (bin_pred v) in \
\        if neg pv then a else f (nat pv) (nat_rec a f (nat pv)))";
by (case_tac "(number_of v)::nat" 1);
by (ALLGOALS (asm_simp_tac
              (simpset() addsimps [Let_def, neg_number_of_bin_pred_iff_0])));
by (asm_full_simp_tac (simpset() addsplits [split_if_asm]) 1);
qed "nat_rec_number_of";

Goal "nat_rec a f (number_of v + n) = \
\       (let pv = number_of (bin_pred v) in \
\        if neg pv then nat_rec a f n \
\                  else f (nat pv + n) (nat_rec a f (nat pv + n)))";
by (stac add_eq_if 1);
by (asm_simp_tac
    (simpset() addsplits [nat.split]
               addsimps [numeral_1_eq_Suc_0 RS sym, Let_def, 
                  neg_imp_number_of_eq_0, neg_number_of_bin_pred_iff_0]) 1);
qed "nat_rec_add_eq_if";

Addsimps [nat_rec_number_of, nat_rec_add_eq_if];


(** For simplifying  # m - Suc n **)

Goal "m - Suc n = (m - 1) - n";
by (simp_tac (numeral_ss addsplits [nat_diff_split]) 1);
qed "diff_Suc_eq_diff_pred";

(*Obsolete because of natdiff_cancel_numerals
    Addsimps [inst "m" "number_of ?v" diff_Suc_eq_diff_pred];
  It LOOPS if Numeral1 is being replaced by 1.
*)


(** Evens and Odds, for Mutilated Chess Board **)

(*Case analysis on b<2*)
Goal "(n::nat) < 2 ==> n = 0 | n = Suc 0";
by (arith_tac 1);
qed "less_2_cases";

Goal "Suc(Suc(m)) mod 2 = m mod 2";
by (subgoal_tac "m mod 2 < 2" 1);
by (Asm_simp_tac 2);
be (less_2_cases RS disjE) 1;
by (ALLGOALS (asm_simp_tac (simpset() addsimps [Let_def, mod_Suc, nat_1])));
qed "mod2_Suc_Suc";
Addsimps [mod2_Suc_Suc];

Goal "!!m::nat. (0 < m mod 2) = (m mod 2 = 1)";
by (subgoal_tac "m mod 2 < 2" 1);
by (Asm_simp_tac 2);
by (auto_tac (claset(), simpset() delsimps [mod_less_divisor]));
qed "mod2_gr_0";
Addsimps [mod2_gr_0];

(** Removal of small numerals: Numeral0, Numeral1 and (in additive positions) 2 **)

Goal "2 + n = Suc (Suc n)";
by (Simp_tac 1);
qed "add_2_eq_Suc";

Goal "n + 2 = Suc (Suc n)";
by (Simp_tac 1);
qed "add_2_eq_Suc'";

Addsimps [numeral_0_eq_0, numeral_1_eq_1, add_2_eq_Suc, add_2_eq_Suc'];

(*Can be used to eliminate long strings of Sucs, but not by default*)
Goal "Suc (Suc (Suc n)) = 3 + n";
by (Simp_tac 1);
qed "Suc3_eq_add_3";


(** To collapse some needless occurrences of Suc 
    At least three Sucs, since two and fewer are rewritten back to Suc again!

    We already have some rules to simplify operands smaller than 3.
**)

Goal "m div (Suc (Suc (Suc n))) = m div (3+n)";
by (simp_tac (simpset() addsimps [Suc3_eq_add_3]) 1);
qed "div_Suc_eq_div_add3";

Goal "m mod (Suc (Suc (Suc n))) = m mod (3+n)";
by (simp_tac (simpset() addsimps [Suc3_eq_add_3]) 1);
qed "mod_Suc_eq_mod_add3";

Addsimps [div_Suc_eq_div_add3, mod_Suc_eq_mod_add3];

Goal "(Suc (Suc (Suc m))) div n = (3+m) div n";
by (simp_tac (simpset() addsimps [Suc3_eq_add_3]) 1);
qed "Suc_div_eq_add3_div";

Goal "(Suc (Suc (Suc m))) mod n = (3+m) mod n";
by (simp_tac (simpset() addsimps [Suc3_eq_add_3]) 1);
qed "Suc_mod_eq_add3_mod";

Addsimps [inst "n" "number_of ?v" Suc_div_eq_add3_div,
	  inst "n" "number_of ?v" Suc_mod_eq_add3_mod];