(** [] *)

(** **** Exercise: 4 stars, advanced, optional (ev_alternate)  *)
(** In general, there may be multiple ways of defining a
    property inductively.  For example, here's a (slightly contrived)
    alternative definition for [ev]: *)

Inductive ev' : nat -> Prop :=
| ev'_0 : ev' 0
| ev'_2 : ev' 2
| ev'_sum : forall n m, ev' n -> ev' m -> ev' (n + m).(** [] *)

(** **** Exercise: 4 stars, advanced, optional (ev_alternate)  *)
(** In general, there may be multiple ways of defining a
    property inductively.  For example, here's a (slightly contrived)
    alternative definition for [ev]: *)

Inductive ev' : nat -> Prop :=
| ev'_0 : ev' 0
| ev'_2 : ev' 2
| ev'_sum : forall n m, ev' n -> ev' m -> ev' (n + m).(** [] *)

(** **** Exercise: 4 stars, advanced, optional (ev_alternate)  *)
(** In general, there may be multiple ways of defining a
    property inductively.  For example, here's a (slightly contrived)
    alternative definition for [ev]: *)

Inductive ev' : nat -> Prop :=
| ev'_0 : ev' 0
| ev'_2 : ev' 2
| ev'_sum : forall n m, ev' n -> ev' m -> ev' (n + m).(** [] *)

(** **** Exercise: 4 stars, advanced, optional (ev_alternate)  *)
(** In general, there may be multiple ways of defining a
    property inductively.  For example, here's a (slightly contrived)
    alternative definition for [ev]: *)

Inductive ev' : nat -> Prop :=
| ev'_0 : ev' 0
| ev'_2 : ev' 2
| ev'_sum : forall n m, ev' n -> ev' m -> ev' (n + m).

Theorem ev_plus_plus : forall n m p, ev (n+m) -> ev (n+p) -> ev (m+p).