problen comparing node with one variable in xslt

with this.
<xsl:variable name="var_masterinformacion_id">
        <xsl:value-of select= "sn_servicioproyecto/masterinformacion_sel"/>
</xsl:variable>
<xsl:value-of select= "$var_masterinformacion_id"/>

i print the variable value

with this:
<xsl:value-of select= "masterinformacion_padre"/>
i print the node value

but i want to compare tthe variable and the masteriformacion_padre value
and if are the same value print ok
i am trying with this code:
<xsl:for-each select="masterinformacion_padre">
<xsl:choose>
        <xsl:when test=".=$var_masterinformacion_id">ok</xsl:when>
</xsl:choose>
</xsl:for-each>

butr it doesn't run.
can you help me please?
i am working in this problem during 2 days and i cannot resolve it.
can you help me please?
thyanks

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