(** Equality on natural numbers *)

(** * Propositional equality  *)

Fixpoint eq_nat n m : Prop :=
  match n, m with
    | O, O => True
    | O, S _ => False
    | S _, O => False
    | S n1, S m1 => eq_nat n1 m1
  end.

Theorem eq_nat_elim : forall n (P:nat -> Prop), P n -> forall m, eq_nat n m -> P m.