(* dat_better is an inductive predicate that lets us conclude that one tree will produce an approximation that is at least as good as some other tree. *)
Inductive dat_better(A : Set) : DistApproxTree A -> DistApproxTree A -> Prop :=
| dat_better_leaf_None : forall t,
  dat_better t (dat_leaf None)
| dat_better_leaf_Some : forall a,
  dat_better (dat_leaf (Some a)) (dat_leaf (Some a))
| dat_better_internal : forall ta1 ta2 tb1 tb2,
  dat_better ta1 tb1 ->
  dat_better ta2 tb2 ->
  dat_better (dat_internal ta1 ta2) (dat_internal tb1 tb2).(* dat_better is an inductive predicate that lets us conclude that one tree will produce an approximation that is at least as good as some other tree. *)
Inductive dat_better(A : Set) : DistApproxTree A -> DistApproxTree A -> Prop :=
| dat_better_leaf_None : forall t,
  dat_better t (dat_leaf None)
| dat_better_leaf_Some : forall a,
  dat_better (dat_leaf (Some a)) (dat_leaf (Some a))
| dat_better_internal : forall ta1 ta2 tb1 tb2,
  dat_better ta1 tb1 ->
  dat_better ta2 tb2 ->
  dat_better (dat_internal ta1 ta2) (dat_internal tb1 tb2).(* dat_better is an inductive predicate that lets us conclude that one tree will produce an approximation that is at least as good as some other tree. *)
Inductive dat_better(A : Set) : DistApproxTree A -> DistApproxTree A -> Prop :=
| dat_better_leaf_None : forall t,
  dat_better t (dat_leaf None)
| dat_better_leaf_Some : forall a,
  dat_better (dat_leaf (Some a)) (dat_leaf (Some a))
| dat_better_internal : forall ta1 ta2 tb1 tb2,
  dat_better ta1 tb1 ->
  dat_better ta2 tb2 ->
  dat_better (dat_internal ta1 ta2) (dat_internal tb1 tb2).(* dat_better is an inductive predicate that lets us conclude that one tree will produce an approximation that is at least as good as some other tree. *)
Inductive dat_better(A : Set) : DistApproxTree A -> DistApproxTree A -> Prop :=
| dat_better_leaf_None : forall t,
  dat_better t (dat_leaf None)
| dat_better_leaf_Some : forall a,
  dat_better (dat_leaf (Some a)) (dat_leaf (Some a))
| dat_better_internal : forall ta1 ta2 tb1 tb2,
  dat_better ta1 tb1 ->
  dat_better ta2 tb2 ->
  dat_better (dat_internal ta1 ta2) (dat_internal tb1 tb2).

Lemma dat_better_trans : forall (A : Set)(t1 t2 : DistApproxTree A), dat_better t1 t2 -> forall t3, dat_better t2 t3 -> dat_better t1 t3.