Goal:
    _z_ : VSet.t  x0 : V.t  x1 : V.t  x2 : V.t  a : V.t  H0 : VSet.In a _z_
  ============================
   (x1 = a)


DEBUG:Going to execute:
autorewrite with set_eq_simpl in *
Level 5: Backtrace:

No matching clauses for match.