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]).