[xsl] Selecting an attribute vale from an external file

["Mark" <mark@xxxxxxxxxxxx>]

I have two files. In the main file is an element
<CatalogNumber>14</CatalogNumber>

The second file contains an unordered sequence of elements like
<Number number="14" name="ceskC= krumlov"></Number>

I want to add an element to the main file
<StampName>ceskC= krumlov</StampName

by selecting the name attribute associated with the number attribute of the 
<Number> element in the second file that matches the current value of 
<CatalogNumber> in the main file.

I tried the below template in my stylesheet but it gives me a set of all the 
number attributes in the second file in the variable bmatching-numberb. I 
have no clue how to proceed. I thought about putting the second file in 
order, then selecting the name attributes into my variable, then indexing 
to, in this instance, the 14th name attribute in the returned set, but that 
seems a bit like brute force.
Clearly I have two problems:
(1) I do not know how to select the matching Number element;
(2) I do not know how select its name attribute

Help or hints would be greatly appreciated.
Mark

My current template:

<xsl:variable name="names" select="document('numbers.xml')"></xsl:variable>

<xsl:template match="CatalogNumber">
 <xsl:copy-of select="."></xsl:copy-of>
  <xsl:variable name="matching-number" 
select="$names/List/Number/@number[.]"></xsl:variable>
  <xsl:element name="StampName">
     <!--<xsl:value-of select=""></xsl:value-of>b>
  </xsl:element>
</xsl:template>