Goal:
    _z_ : VSet.t  x0 : V.t  a : V.t
  ============================
   ((VSet.In a (VSet.add x0 _z_) -> VSet.In a (VSet.add x0 _z_)) /\
    (VSet.In a (VSet.add x0 _z_) -> VSet.In a (VSet.add x0 _z_)))


DEBUG:Going to execute:
match goal with
           | H:forall a : V.t, _ |- _ => clear H
           end