public function postLogin(Request $r)
 {
     $user = Admin::attempt($r->input('email'), $r->input('password'));
     if ($user == null) {
         $user = Enseignant::attempt($r->input('email'), $r->input('password'));
         if ($user != null) {
             $filiere = Enseignant::isChef($user->id);
             if ($filiere != null) {
                 Session::put('user', $user);
                 return redirect('/app/cheffiliere');
             }
         }
     }
     if ($user == null) {
         $user = Etudiant::attempt($r->input('email'), $r->input('password'));
     }
     if ($user != null) {
         Session::put('user', $user);
         return redirect('/app');
     } else {
         return redirect('/');
     }
 }