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


DEBUG:Going to execute:
VSetDecide.MSetDecideAuxiliary.substMSet
Level 1: Backtrace:

No matching clauses for match.