<xsl:for-each> , only loop on half of the elements.

i have a pretty weird use case :

i have a node contained number of elements but late say i got 6 elements i only need to first 3.

<xsl:for-each select="/content/collaborator">
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.
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<xsl:for-each>

i know that  this kind of things should be treated in data source level ...  ,  i'm using apache Fop to print my reports and i use the data that comes thru a webservices so can't modify it ..   any way in my xsl to use only the NUMBER_OF_ELEMENT / 2 ?


PS:inside my <xsl:for-each> i print a table body that contain the data


and thanks