(************)
(* Opposite *)
(************)

Inductive opposite : word -> word -> Prop :=
    opp : forall (u v : word) (b : bool), opposite (bit b u) (bit (negb b) v).(************)
(* Opposite *)
(************)

Inductive opposite : word -> word -> Prop :=
    opp : forall (u v : word) (b : bool), opposite (bit b u) (bit (negb b) v).

Lemma alt_not_opp : forall (u v : word) (b : bool), alt b u -> alt b v -> ~ opposite u v.