[xsl] Assigning serial numbers

["Siddhi Thakkar" <siddhi.thakkar@xxxxxxxxxxxxxx>]

Dear Experts,

I need to create an HTML table of dead links and assign serial numbers to 
it. Here is what my input looks like:

<book>
   <para id="p1"> .....some text..... <a href="p5">.....</a> ...some 
text..... </para>
   <article id="p2"> ......some text..... <a href="p1">......</a> text2 
</article>
   <section id="p3">.....some text....<a 
href="p9">.....</a>...........</section>
</book>

Since two of the href attribute values listed above (p5 and p9) have no 
corresponding id values, these are the dead links. Please note that I have 
got the list of such links, I AM ONLY STUCK AT PROVIDING SERIAL NOS. 
Mentioned below is my XSL code:

<!--CODE START-->
<xsl:output method="html"/>
<xsl:template match="/">
      <table>
          <xsl:apply-templates/>
       </table>
</xsl:template>

<xsl:template match="//a">
       <xsl:for-each select="@href">
               <xsl:if test="not(for $x in //@id return $x[$x=current()])">
                       <tr>
                               <td>
                                   <!-- This is where I would like to write 
the code to assign serial number-->
                               </td>
                               <td>
                                       <xsl:value-of select="current()"/>
                               </td>
                   </tr>
             </xsl:if>
       </xsl:for-each>
</xsl:template>

<xsl:template match="text()"/>
<!--CODE END-->

DESIRED OUTPUT:
<table>
   <tr>
       <td>1</td>
       <td>p5</td>
   </tr>
   <tr>
       <td>2</td>
       <td>p9</td>
   </tr>
</table>

Thanks much,
Siddhi