proposition: Lemma inj_add_abs n m : Z.abs_nat (Z.abs n + Z.abs m) = (Z.abs_nat n + Z.abs_nat m)%nat.
proof: Proof. now rewrite <- !Zabs_N_nat, Zabs2N.inj_add_abs, N2Nat.inj_add. Qed.
imports: Arith_base BinPos BinInt BinNat Pnat Nnat