(* Title: HOL/NatArith.thy
ID: $Id$
Setup arithmetic proof procedures.
*)
theory NatArith = Nat
files "arith_data.ML":
setup arith_setup
(*elimination of `-' on nat*)
lemma nat_diff_split:
"P(a - b::nat) = ((a<b --> P 0) & (ALL d. a = b + d --> P d))"
by (cases "a<b" rule: case_split) (auto simp add: diff_is_0_eq [THEN iffD2])
(*elimination of `-' on nat in assumptions*)
lemma nat_diff_split_asm:
"P(a - b::nat) = (~ (a < b & ~ P 0 | (EX d. a = b + d & ~ P d)))"
by (simp split: nat_diff_split)
ML {*
val nat_diff_split = thm "nat_diff_split";
val nat_diff_split_asm = thm "nat_diff_split_asm";
(* TODO: use this for force_tac in Provers/clasip.ML *)
fun add_arith cs = cs addafter ("arith_tac", arith_tac);
*}
lemmas [arith_split] = nat_diff_split split_min split_max
end