Definition beq: forall (A: Type), (A -> A -> bool) -> t A -> t A -> bool := PTree.beq.

Theorem beq_sound: forall (A: Type) (eqA: A -> A -> bool) (t1 t2: t A), beq eqA t1 t2 = true -> forall (x: elt), match get x t1, get x t2 with | None, None => True | Some y1, Some y2 => eqA y1 y2 = true | _, _ => False end.