Erreur php/mysql aide please

Bonjour,
bonjour c'est un code de tchat je n'arrive à afficher donc je compte sur vous pour me faire la correction .
code:
chat.php

<?php
function tchat(){
$connect=mysql_connect("localhost","root","root");
mysql_select_db("chat",$connect);
$query=mysql_query("SELECT DISTINCT pseudo FROM lettre");
$nombre_connecte=mysql_num_rows($query);
echo"",$nombre_connecte," connecté(s) sur le chat<br><br>";
$affich_dialogue="SELECT * FROM lettre ORDER BY id DESC";
$chat=mysql_query($affich_dialogue,$connect);
while($tab=mysql_fetch_array($chat,MYSQL_ASSOC)){
$pseudo = stripslashes($tab['pseudo']);
$com = stripslashes($tab['com']);

</head>
<body>
<?php
$connect=mysql_connect("localhost","root","root");
mysql_select_db("chat",$connect);

$temps = 300;

$heure_debut_chat = time();

$date = date("d-m-y");

$heure = date("H\hi");

$heure_fin_chat = $heure_debut_chat-$temps;

mysql_query("DELETE FROM lettr WHERE time<'$heure_fin_chat'");

if($submit){

if(empty($pseudo) or empty($com) or $pseudo=='Votre
pseudo'){
tchat();
exit();
}else{
$pseudo = trim($pseudo);
$pseudo = AddSlashes($pseudo);
$pseudo = strip_tags($pseudo);
$com = strip_tags($com);
$com = AddSlashes($com);
$insert_text="INSERT INTO lettre(time,date,heure,pseudo,com)";
$insert_text.="VALUES('$heure_debut_chat','$date','$heure','$pseudo','$com')";
mysql_query($insert_text,$connect);
}
}
tchat();

mysql_close();
?>
</body>
</html>

voilà l'erreur qui 'il m'affiche.
Notice: Undefined variable: submit in c:\program files\easyphp1-7\www\assisdicko\chat.php on line 48
0 connecté(s) sur le chat

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