Global Variables referencing each other

Should variables defined globally be able to refer to each other? eg

<xsl:variable name="a">1</xsl:variable>
<xsl:variable name="b">2</xsl:variable>
<xsl:variable name="c"><xsl:value-of select="$a + $b"/></xsl:variable>

Im getting a variable out of scope error for a situation like the one above.

Thanks,

Steve.


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