Goal:
    s : VSet.t  x : VSet.elt  H : VSet.In x s  y : VSet.elt  H0 : VSet.In y s
  ============================
   (x = y \/ VSet.In y s)


DEBUG:Going to execute:
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