Filter XML data using a custom markup language

I am trying to write a document that can help filter data from another XML document. For instance.

<document>
    <filter>
        <what>
            <include>
                <marital_staus/>
                <ms>single</ms> <!--nog = no of groups-->
                <include>
                    <memberofgroups/>
                    <gn>Football club</gn> <!--user is a member of this club-->
                </include>
            </include>
        </what>
    </filter>

    <users>
            <user>
                <name>
                    <first>abc</first>
                    <last>xyz</last>
                </name>
                <dob>12/02/1987</dob>
                <marital_status>married</marital_status>
                <groups>
                    <member_of_group>Chess Club</member_of_group>
                    <member_of_group>Football club</member_of_group>
                </groups>
            </user>

            <user>
                <name>
                    <first>aaa</first>
                    <last>bbb</last>
                </name>
                <dob>14/03/1987</dob>
                <marital_status>single</marital_status>
                <groups>
                    <member_of_group>Chess Club</member_of_group>
                    <member_of_group>Football club</member_of_group>
                </groups>
            </user>

             <user>
                <name>
                    <first>fff</first>
                    <last>nnn</last>
                </name>
                <dob>12/6/1983</dob>
                <marital_status>single</marital_status>
                <groups>
                    <member_of_group>Chess Club</member_of_group>
                    <member_of_group>Cultural Association</member_of_group>
                </groups>
            </user>
     </users>
</document>

I want this code to do this, first, select the users who are members of the football club, and then select the users who are single from them. But I can't figure out how to write a stylesheet for this. I wrote this:

<xsl:template name="temp">
        <xsl:param name="a1"/>
        <xsl:param name="pro"/>
        <xsl:choose>
            <xsl:when test="$pro = 'marital_status'">
                <xsl:for-each select="/document/users/user">
                    <xsl:if test="marital_status=$a1">
                        <xsl:value-of select="."/>
                    </xsl:if>                
                </xsl:for-each>
            </xsl:when>
            <xsl:when test="$pro = 'memberofgroups'">
            <xsl:for-each select="/document/users/user">
                <xsl:for-each select="./groups/member_of_group">
                    <xsl:if test=".=$a1">
                        <xsl:value-of select="."/>
                    </xsl:if>
                </xsl:for-each>
            </xsl:for-each>
        </xsl:when>
        </xsl:choose>
    </xsl:template>
<xsl:template match="include">
        <xsl:call-template name="temp">
            <xsl:with-param name="a1">
                <xsl:apply-templates select="*[2]"/>
            </xsl:with-param>
        </xsl:call-template>
    </xsl:template>

When calling the template, I pass the correct values, I suppose.

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