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(*         *   The Coq Proof Assistant / The Coq Development Team       *)
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(*    //   *    This file is distributed under the terms of the         *)
(*         *     GNU Lesser General Public License Version 2.1          *)
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(** Binary Integers : Parity and Division by Two *)
(** Initial author : Pierre Crégut (CNET, Lannion, France) *)
(** THIS FILE IS DEPRECATED. It is now almost entirely made of compatibility formulations for results already present in BinInt.Z. *)
Open Scope Z_scope.
(** Historical formulation of even and odd predicates, based on case analysis. We now rather recommend using [Z.Even] and [Z.Odd], which are based on the exist predicate. *)
Definition Zeven (z:Z) :=
match z with
| Z0 => True
| Zpos (xO _) => True
| Zneg (xO _) => True
| _ => False
end.
Definition Zodd (z:Z) :=
match z with
| Zpos xH => True
| Zneg xH => True
| Zpos (xI _) => True
| Zneg (xI _) => True
| _ => False
end.

Theorem Zeven_ex_iff n : Zeven n <-> exists m, n = 2*m.