Goal:
    _z_ : VSet.t  a : V.t
  ============================
   (VSet.In a _z_ <-> VSet.In a _z_)


DEBUG:Going to execute:
cbv beta zeta in *
Level 1: Backtrace:

Cannot find any non-recursive equality over _z_.
Level 1: Backtrace:

Cannot find any non-recursive equality over _z_.
Level 0: Backtrace:

Cannot find any non-recursive equality over _z_.