Notation Zeven_bool_succ := Z.even_succ (only parsing).Notation Zeven_bool_pred := Z.even_pred (only parsing).Notation Zodd_bool_succ := Z.odd_succ (only parsing).Notation Zodd_bool_pred := Z.odd_pred (only parsing).

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