Fatal error: Call to undefined function seo() in /home/.../public_html/urunler.php on line 59 hatası alıyorum ne yapmam gerekiyor arkadaşlar?

<?php
session_start();
include("inc/head.php"); 
include("inc/public.php"); 
d_connect(); 
?>
   <?php   
  if(@$_GET["dil"]=="en"){
    $_SESSION["dil"] = "en"; 
  }      
   elseif(@$_GET["dil"]=="tr"){
    $_SESSION["dil"] = "tr"; 
  }else{       
    if(@$_SESSION["dil"]==""){
      $_SESSION["dil"] = "tr"; 
    }  
  } 
  
  include_once("inc/defines.php"); 
  ?>
  
	<?php
   include("inc/menu.php"); 
  ?>
		
		<div class="container">
			<div class="row">
				<div class="span12">
                	<div id="inner_title">
                        <h1><?php echo Urunler_Sabit ;?></h1>
                         
                    </div><!--/inner title-->
				</div><!--/span12-->
			</div><!--/row-->
		</div><!--/container-->
		
		<div id="content">
			<div class="container">
				 
				
                <div id="filterSection" data-perrow="4">
                    <div class="row grid-listings">
                    
                     <?php
                    $sql_urun="SELECT * FROM kategoriler WHERE kat_tip='1'" ;
                    $sql_urun_my=mysql_query($sql_urun);
                    while($kat=mysql_fetch_array($sql_urun_my)){
                      $kat_ad=$kat[Kat_ad] ;
                      $kat_resim=$kat['kat_resim'];
                      $kat_id=$kat['kat_id'];
                     echo' 
                    <div class="span3 filterable web seo">
                          <img src="dosyalar/kategoriler/'.$kat_resim.'" alt="three" />
                          <div class="white-bg box-top-fix">
                          <h4>'.$kat_ad.'</h4>                                  
                               
                              
                          <div class="aboutsocial">
                                  <a href="'.seo($kat_ad).'-'.Urun_link.'-'.$kat_id.'.html">'.Urunler_Sabit2.'</a>
                              </div><!--/aboutsocial-->
                          </div><!--/white bg-->
                    </div><!--/span 3-->';                      
                     
                    } 
                   
                    
                     ?>
  
                        
                    </div><!--/row-->
         
                </div>
			</div><!--/container-->
			
			<br>
	</div><!--/hero-->
		 
		
	<?php
   include("inc/footer.php"); 
  ?>
		<script src="http://code.jquery.com/jquery-latest.js"></script>
		<script src="_assets/js/bootstrap.min.js"></script>
        <script type="text/javascript" src="_assets/js/filter.js"></script>
        
        <!-- Latest Tweets -->
        <script type="text/javascript" src="_assets/js/twitter.js"></script>
        <script type="text/javascript">
		jQuery(document).ready(function() {
			jQuery('#latest_tweets').jtwt({
				username: 'designedbydash',
				count: '2',
				loader_text: 'Loading Tweets...'
			});
		});
		</script>
</body>
</html>