Goal:
  
  s0 : VSet.t
  s' : VSet.t
  x : V.t
  d : DisjointAdd x s0 s'
  a : VSet.elt
  Ha : VSet.In a s' /\ ~ VSet.E.eq a x
  H : VSet.In a s' <-> x = a \/ VSet.In a s0
  ============================
   (VSet.In a s0)


DEBUG:Going to execute:
repeat
            (match reverse goal with
             | id:?X1
               |- _ =>
                   <Coq.Init.Tauto.is_conj> flags X1; elim id; do 2 intro;
                    clear id
             | id:_ <-> _ |- _ => elim id; do 2 intro; clear id
             | id:~ _ |- _ => red in id
             | id:?X1
               |- _ =>
                   <Coq.Init.Tauto.is_disj> flags X1; elim id; intro; clear
                    id
             | _ =>
                 <Coq.Init.Tauto.find_cut>
                  ltac:(fun id0 id1 X2 =>
                          assert X2; [ exact (id0 id1) | clear id0 ])
             | id:?X1 -> ?X2
               |- _ =>
                   <Coq.Init.Tauto.is_unit_or_eq> flags X1; Ltac.cut X2;
                    [ intro; clear id
                    | Ltac.cut X1; [ exact id | constructor 1; fail ] ]
             | id:?X1 -> ?X2
               |- _ =>
                   <Coq.Init.Tauto.flatten_contravariant_conj> flags X1 X2 id
             | id:?X1 <-> ?X2 -> ?X3
               |- _ =>
                   assert ((X1 -> X2) -> (X2 -> X1) -> X3) by
                    (do 2 intro; apply id; Ltac.split; Ltac.assumption);
                    clear id
             | id:?X1 -> ?X2
               |- _ =>
                   <Coq.Init.Tauto.flatten_contravariant_disj> flags X1 X2 id
             | |- ?X1 => <Coq.Init.Tauto.is_conj> flags X1; Ltac.split
             | |- _ <-> _ => Ltac.split
             | |- ~ _ => red
             end; <Coq.Init.Tauto.not_dep_intros>)
Level 0: Backtrace:

No matching clauses for match.