(* Successor relation  *)

Inductive Successor : Tree -> Tree -> Prop :=
  | successor_refl : forall t : Tree, Successor t t
  | successor_trans :
      forall t0 t1 : Tree,
      In_Forest t1 (successors t0) ->
      forall t2 : Tree, Successor t2 t1 -> Successor t2 t0.(* Successor relation  *)

Inductive Successor : Tree -> Tree -> Prop :=
  | successor_refl : forall t : Tree, Successor t t
  | successor_trans :
      forall t0 t1 : Tree,
      In_Forest t1 (successors t0) ->
      forall t2 : Tree, Successor t2 t1 -> Successor t2 t0.(* Successor relation  *)

Inductive Successor : Tree -> Tree -> Prop :=
  | successor_refl : forall t : Tree, Successor t t
  | successor_trans :
      forall t0 t1 : Tree,
      In_Forest t1 (successors t0) ->
      forall t2 : Tree, Successor t2 t1 -> Successor t2 t0.

Lemma succs_refl : forall t : Tree, Successor t t.