Library Coq.setoid_ring.NArithRing
Require Export Ring.
Require Import BinPos BinNat.
Import InitialRing.
Set Implicit Arguments.
Ltac Ncst t :=
match isNcst t with
true => t
| _ => constr:(NotConstant)
end.
Add Ring Nr : Nth (decidable Neqb_ok, constants [Ncst]).