Indexing in xsl

Hi,
I wanted to know how (if) we can do indexing on a element name
I have a input xml:
<orders>
	<order id="1">
	<order id="2">
	<order id="3">
	<order id="4">
	.
<orders>
which has to be converted to 
<orders order1-id="1" order2-id="2" order2-id="3" order2-id="4" />

Is this right?
		<xsl:attribute name="{concat(local-name(), 'var', '-','id')}"> 
			<xsl:value-of select="@id"/>
		</xsl:attribute>

How do I change the val of 'var'
Any pointers on this?

Thanks,
~Bharathy

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