xsl:variable doesn't work here

Instead of

    <xsl:if test=".//article[.//author='C. J. Date']">
    ..
     <xsl:copy-of select=".//article[.//author='C. J. Date']"/>

i want to store the condition in a variable condition and write

    <xsl:variable name="condition">.//article[.//author='C. J.
Date']</xsl:variable>


    <xsl:if test="$condition">
    ..
     <xsl:copy-of select="$condition"/>

But this does not work. I also tried {$condition} instead of $condition.

Whats wrong?

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 ROBERT SÖSEMANN  (robert.soesemann@xxxxxx)

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