Goal:
    x : V.t  p : VSet.t  a : V.t  H : VSet.In a p -> False  H1 : VSet.In a p
  ============================
   False


DEBUG:Going to execute:
repeat
            match goal with
            | |- ?X1 -> ?X2 => intro
            | |- ~ _ => unfold not at 1; intro
            end