Goal:
  
  s : VSet.t
  s' : VSet.t
  s'' : VSet.t
  x : V.t
  hadd : VSetProp.Add x s s'
  hin : ~ VSet.In x s
  H : ~ VSet.In x s''
  ============================
   (~ VSet.In x (VSet.union s s''))


DEBUG:Going to execute:
match goal with
           | H:?P
             |- _ =>
                 match type of P with
                 | Prop =>
                     match goal with
                     | H':context [ H ] |- _ => clear dependent H'
                     end
                 | _ => fail
                 end; VSetDecide.MSetDecideAuxiliary.no_logical_interdep
           | _ => idtac
           end