Problem with xsl:if

I have the following XML Document:

<?xml version="1.0" encoding="UTF-8"?>
   <input>
      <add class-name="User">
         <add-attr attr-name="jkuSLABS">
            <value>90</value>
         </add-attr>
         <add-attr attr-name="jkuSLART">
            <value>50</value>
         </add-attr>
         <add-attr attr-name="jkuPeHabd">
            <value type="string">7777-33-11</value>
         </add-attr>
      </add>
   </input>


What Id like to to is the get an output document which should contain
the 
         <add-attr attr-name="jkuPeHabd">
            <value type="string">7777-33-11</value>
         </add-attr>
only, if the jkuSLABS=90 AND jkuSLART=50. Otherwise the 3 lines should
be omitted.

I thought of the following, but I think I am misunderstanding
something:

        <xsl:template match="node()|@*">
                <xsl:copy>
                        <xsl:apply-templates select="@*|node()"/>
                </xsl:copy>
        </xsl:template>
        <xsl:template match="*[(_at_)attr-name='jkuPeHabd']">
                <xsl:variable name="slart"
select="//*[(_at_)attr-name='jkuPeBeschSAP22SLART']//value"/>
                <xsl:variable name="slabs"
select="//*[(_at_)attr-name='jkuPeBeschSAP22SLABS']//value"/>

                <xsl:if test="($slart!='50')   or   ($slabs!='90')">
                </xsl:if>
        </xsl:template>

As far as I can see the if never gets true, but still if it would be
true, I would need some "else" operation. Maybe you can give me a hint
how to solve this.

Thank you in advance,
Gerald