..Ho modificato in questo modo ma ancora niente,non riesco a cambiare il valore di $tt

Codice PHP:
 //se è stato cliccato il tasto per nascondere/mostrare la textbox
      
if(isset($_POST['title_subm']))
         {
           
            
$tt$_SESSION["tt"];

            if(
$tt == 'n' ){
            
$values_array["tt"]= 's';}
            else{
            
$values_array["tt"]='n';}     
         }
          
          else{
                if(
$values_array["tt"]==''){
                 
$values_array["tt"]='n';
                 
$_SESSION["tt"] = $values_array["tt"];
                 
$tt$_SESSION["tt"];}
                else{
                 
$_SESSION["tt"] = $values_array["tt"];
                 
$tt=$_SESSION["tt"];}
               } 
e ho creato questo form:
Codice PHP:

    <form name="subm_m" method="post" action="<?php echo"$current_page";?>">
    <td bgcolor="#00FF99"><select name="sel_friend" > <?php include("_include/select_fr.php"); ?> </select></td>
    <td width="450" bgcolor="#00FF99"><div id="title_box">

                     <input type="submit" value="<?php if($tt=='s'){ echo"Rimuovi Titolo";} if($tt=='n'){echo"Aggiungi Titolo"; }?>" name="title_subm"   />

                     <?php if($tt=='s'){ ?>
                     

 <input type="text" name="titolo" value="<?=$_SESSION["titolo"]?>" /></p>
                     <?php ?>

                     </div></td>
    <td width="185" align="center" bgcolor="#00FF99"><input type="submit" value="Invia!" name="rapid_mess" /></td>
Avete questa idea?