Goal:
  
  x : V.t
  s : VSet.t
  s' : VSet.t
  z : VSet.elt
  H : VSetProp.Add x s (VSet.remove z s')
  H0 : VSet.In x s -> False
  i : VSet.elt
  H1 : VSet.In i s
  ============================
   (VSet.In i s)


DEBUG:Going to execute:
fun flags =>
             match reverse goal with
             | |- ?X1 =>
                   <Coq.Init.Tauto.is_unit_or_eq> flags X1; constructor 1
             | H:?X1 |- _ => <Coq.Init.Tauto.is_empty> flags X1; elim H
             | _ => Ltac.assumption
             end