Goal:
    x : V.t  y : V.t  p : VSet.t  a : V.t
  ============================
   ((VSet.In a (VSet.add x (VSet.add y p)) ->
     VSet.In a (VSet.add y (VSet.add x p))) /\
    (VSet.In a (VSet.add y (VSet.add x p)) ->
     VSet.In a (VSet.add x (VSet.add y p))))


DEBUG:Going to execute:
repeat match goal with
                  | H:forall a : V.t, _ |- _ => clear H
                  end
Level 1: Backtrace:

No matching clauses for match.