Goal:
  
  s : VSet.t
  s'' : VSet.t
  x : V.t
  hin : ~ VSet.In x s
  H : VSet.In x s \/ VSet.In x s''
  ============================
   (VSet.In x s'')


DEBUG:Going to execute:
intuition VSetDecide.MSetDecideAuxiliary.fsetdec_rec ||
             fail 1 "because the goal is beyond the scope of this tactic"