Goal:
  
  G : t
  s0 : VSet.t
  s' : VSet.t
  x : V.t
  y : V.t
  z : V.t
  d : DisjointAdd x s0 s'
  e : EdgeOf x y
  p : SPath s0 y z
  IHp : forall s' : VSet.t, VSet.Subset s0 s' -> SPath s' y z
  s'0 : VSet.t
  Hs : VSet.Subset s' s'0
  u : VSet.elt
  Hu : VSet.In u s0
  ============================
   (x = u \/ VSet.In u s0)


DEBUG:Going to execute:
fun flags t_reduce t_solver =>
             let rec t_tauto_intuit :=
              <Coq.Init.Tauto.simplif> flags;
               <Coq.Init.Tauto.axioms> flags ||
                 match reverse goal with
                 | id:(?X1 -> ?X2) -> ?X3
                   |- _ =>
                       Ltac.cut X3;
                        [ intro; clear id; t_tauto_intuit
                        | Ltac.cut (X1 -> X2);
                           [ exact
                           id
                           | generalize (fun y : X2 => id (fun x : X1 => y));
                              intro; clear id; (solve 
                              [ t_tauto_intuit ]) ] ]
                 | id:~ ?X1 -> ?X3
                   |- _ =>
                       Ltac.cut X3;
                        [ intro; clear id; t_tauto_intuit
                        | Ltac.cut (~ X1);
                           [ exact
                           id
                           | clear id; intro; (solve [ t_tauto_intuit ]) ] ]
                 | |- ?X1 =>
                       <Coq.Init.Tauto.is_disj> flags X1; (solve
                        [ Ltac.left; t_tauto_intuit
                        | Ltac.right; t_tauto_intuit ])
                 end ||
                   match goal with
                   | |- _ -> _ => intro; t_tauto_intuit
                   | |- _ => t_reduce; t_solver
                   end || t_solver
             in
             t_tauto_intuit