Call template when values match

i have the following xml input

<RS>
      <SAvailRQ>
            <Code>AL</Code>
            <FNum>131</FNum>
      </SAvailRQ>
<SMapRS>
  <SMapResponses>
      <SMapResponse>
            <SegInfo FNum="131">
            <Departure LocationCode="MIA"/>
            <Arrival LocationCode="LAX"/>
            <Marketing Code="AL"/>
            </SegInfo>
      </SMapResponse>
      <SMapResponse>
            <SegInfo FNum="118">
            <Departure LocationCode="LAX"/>
            <Arrival LocationCode="MIA"/>
            <Marketing Code="AL"/>
            </SegInfo>      
      </SMapResponse>      
   </SMapResponses>
</SMapRS>      
</RS>      

I need logic such that if RS/SAvailRQ/FNum matches that found in RS/SMapRS/SMapResponses/SMapResponse/SegInfo/@FNum
to call a template to build an Info node on that match only.

Currently, I have the following
    <xsl:apply-templates select="SMapResponses/SMapResponse/SegInfo"/>
but this loops twice (bc there are 2 SegInfo), I do not want that. I just want it to go into this template for the matching record(s) and then process data for that matching record only.

So how do I apply a for-each statement that will find matching FNum in SAvailRQ with that in SMapResponse and have that template called for that instance(s) only?


basically a filter.