Ltac ct := trivial with ct.Inductive ct: comparison -> comparison -> comparison -> Prop :=
  | ct_xxx: forall x, ct x  x  x
  | ct_xex: forall x, ct x  Eq x
  | ct_exx: forall x, ct Eq x  x
  | ct_glx: forall x, ct Gt Lt x
  | ct_lgx: forall x, ct Lt Gt x.Inductive ct: comparison -> comparison -> comparison -> Prop :=
  | ct_xxx: forall x, ct x  x  x
  | ct_xex: forall x, ct x  Eq x
  | ct_exx: forall x, ct Eq x  x
  | ct_glx: forall x, ct Gt Lt x
  | ct_lgx: forall x, ct Lt Gt x.Inductive ct: comparison -> comparison -> comparison -> Prop :=
  | ct_xxx: forall x, ct x  x  x
  | ct_xex: forall x, ct x  Eq x
  | ct_exx: forall x, ct Eq x  x
  | ct_glx: forall x, ct Gt Lt x
  | ct_lgx: forall x, ct Lt Gt x.Inductive ct: comparison -> comparison -> comparison -> Prop :=
  | ct_xxx: forall x, ct x  x  x
  | ct_xex: forall x, ct x  Eq x
  | ct_exx: forall x, ct Eq x  x
  | ct_glx: forall x, ct Gt Lt x
  | ct_lgx: forall x, ct Lt Gt x.Inductive ct: comparison -> comparison -> comparison -> Prop :=
  | ct_xxx: forall x, ct x  x  x
  | ct_xex: forall x, ct x  Eq x
  | ct_exx: forall x, ct Eq x  x
  | ct_glx: forall x, ct Gt Lt x
  | ct_lgx: forall x, ct Lt Gt x.

Lemma compare_x_Leaf: forall s, compare s Leaf = if is_empty s then Eq else Gt.