(** * Elements *)

Notation eqk := (PX.eqk (elt:= elt)).Notation eqke := (PX.eqke (elt:= elt)).Notation ltk := (PX.ltk (elt:= elt)).

Lemma elements_node : forall (t1 t2:t elt) x e z l, elements t1 ++ (x,e) :: elements t2 ++ l = elements (Node t1 x e t2 z) ++ l.