(* Beta reduction *)
Inductive red1 : lambda -> lambda -> Prop :=
  | beta : forall M N : lambda, red1 (App (Abs M) N) (subst N M)
  | abs_red : forall M N : lambda, red1 M N -> red1 (Abs M) (Abs N)
  | app_red_l :
      forall M1 N1 : lambda,
      red1 M1 N1 -> forall M2 : lambda, red1 (App M1 M2) (App N1 M2)
  | app_red_r :
      forall M2 N2 : lambda,
      red1 M2 N2 -> forall M1 : lambda, red1 (App M1 M2) (App M1 N2).(* Beta reduction *)
Inductive red1 : lambda -> lambda -> Prop :=
  | beta : forall M N : lambda, red1 (App (Abs M) N) (subst N M)
  | abs_red : forall M N : lambda, red1 M N -> red1 (Abs M) (Abs N)
  | app_red_l :
      forall M1 N1 : lambda,
      red1 M1 N1 -> forall M2 : lambda, red1 (App M1 M2) (App N1 M2)
  | app_red_r :
      forall M2 N2 : lambda,
      red1 M2 N2 -> forall M1 : lambda, red1 (App M1 M2) (App M1 N2).(* Beta reduction *)
Inductive red1 : lambda -> lambda -> Prop :=
  | beta : forall M N : lambda, red1 (App (Abs M) N) (subst N M)
  | abs_red : forall M N : lambda, red1 M N -> red1 (Abs M) (Abs N)
  | app_red_l :
      forall M1 N1 : lambda,
      red1 M1 N1 -> forall M2 : lambda, red1 (App M1 M2) (App N1 M2)
  | app_red_r :
      forall M2 N2 : lambda,
      red1 M2 N2 -> forall M1 : lambda, red1 (App M1 M2) (App M1 N2).(* Beta reduction *)
Inductive red1 : lambda -> lambda -> Prop :=
  | beta : forall M N : lambda, red1 (App (Abs M) N) (subst N M)
  | abs_red : forall M N : lambda, red1 M N -> red1 (Abs M) (Abs N)
  | app_red_l :
      forall M1 N1 : lambda,
      red1 M1 N1 -> forall M2 : lambda, red1 (App M1 M2) (App N1 M2)
  | app_red_r :
      forall M2 N2 : lambda,
      red1 M2 N2 -> forall M1 : lambda, red1 (App M1 M2) (App M1 N2).(* Beta reduction *)
Inductive red1 : lambda -> lambda -> Prop :=
  | beta : forall M N : lambda, red1 (App (Abs M) N) (subst N M)
  | abs_red : forall M N : lambda, red1 M N -> red1 (Abs M) (Abs N)
  | app_red_l :
      forall M1 N1 : lambda,
      red1 M1 N1 -> forall M2 : lambda, red1 (App M1 M2) (App N1 M2)
  | app_red_r :
      forall M2 N2 : lambda,
      red1 M2 N2 -> forall M1 : lambda, red1 (App M1 M2) (App M1 N2).(* Transitive closure of red1 *)
Inductive red : lambda -> lambda -> Prop :=
  | one_step_red : forall M N : lambda, red1 M N -> red M N
  | refl_red : forall M : lambda, red M M
  | trans_red : forall M N P : lambda, red M N -> red N P -> red M P.(* Transitive closure of red1 *)
Inductive red : lambda -> lambda -> Prop :=
  | one_step_red : forall M N : lambda, red1 M N -> red M N
  | refl_red : forall M : lambda, red M M
  | trans_red : forall M N P : lambda, red M N -> red N P -> red M P.(* Transitive closure of red1 *)
Inductive red : lambda -> lambda -> Prop :=
  | one_step_red : forall M N : lambda, red1 M N -> red M N
  | refl_red : forall M : lambda, red M M
  | trans_red : forall M N P : lambda, red M N -> red N P -> red M P.(* Transitive closure of red1 *)
Inductive red : lambda -> lambda -> Prop :=
  | one_step_red : forall M N : lambda, red1 M N -> red M N
  | refl_red : forall M : lambda, red M M
  | trans_red : forall M N P : lambda, red M N -> red N P -> red M P.

Lemma red_appr : forall M M' : lambda, red M M' -> forall N : lambda, red (App N M) (App N M').