XPath help

What XPath do I use to specify "elements which are neither <a> nor <b>"?
Here's an example:
 
<top>
    <a>1</a> 
    <a>2</a> 
    <a>3</a> 
    <b>1</b> 
    <b>2</b>
    <c>1</c> 
    <c>2</c> 
    <c>3</c> 
    <c>4</c> 
    <c>5</c>
    <d>1</d> 
    <d>2</d>
</top>
 
I would like to iterate over all but the <a> and <b> elements, in this case,
<c> and <d> elements.
 
Something like this is what I had in mind:
 
<xsl:template match="top">
    <xsl:for-each select="*[not(a|b)]">
        <!-- do something -->
    </xsl:for-each>
</xsl:template>
 
But it does not seem to work. I can't find the syntax for this, but it can't
be that hard.  Suggestions?
 
 
William Bagby.

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list