Goal:
    x : VSet.elt  p : VSet.t  H : ~ VSet.In x p
  ============================
   (VSet.Equal (VSet.remove x (VSet.add x p)) p)


DEBUG:Going to execute:
match goal with
           | H':context [ H ] |- _ => clear dependent H'
           end
DEBUG LTAC Evaluated term: (~ VSet.In x p)
DEBUG LTAC Evaluated term: Prop
Level 3: type of P
 has value 
Prop