Re: Compare logical expressions with XPath/XSLT

if I understood you correctly you have a fixed number of boolean
variables (3 here) so you can enumerate the truth table of  each
project and want to know that the expression for the sub project is
never true if the expression for the main project is false.

this is not, to put it mildly, well tested but I get

$ saxon9 -it:main prg.xsl
project 1 and 2
false
project 1 and 3
true


from the following which assumes AND and OR always have exactly two
children and that my typing is accurate, neither of which assumption
may be true...

<xsl:stylesheet version="2.0"
        xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
        xmlns:xs="http://www.w3.org/2001/XMLSchema"
        xmlns:f="data:,f">

 <xsl:variable name="defs" as="element()">
  <defs>
  <def name="project-1">
    <set>
      <AND>
        <OR>
          <item required="false">A</item>
          <item required="false">B</item>
        </OR>
        <item required="false">C</item>
      </AND>
    </set>
  </def>
  <def name="project-2">
    <set>
      <OR>
        <item required="true">A</item>
        <item required="true">C</item>
      </OR>
    </set>
  </def>
  <def name="project-3">
    <set>
      <item required="false">C</item>
    </set>
  </def>
</defs>
</xsl:variable>

<xsl:template name="main">
 <xsl:message select="'project 1 and 2'"/>
 <xsl:message select="f:check($defs/def[@name='project-1']/set/*,$defs/def[@name='project-2']/set/*)"/>
 <xsl:message select="'project 1 and 3'"/>
 <xsl:message select="f:check($defs/def[@name='project-1']/set/*,$defs/def[@name='project-3']/set/*)"/>
</xsl:template>

<xsl:function name="f:check" as="xs:boolean">
 <xsl:param name="p1" as="element()"/>
 <xsl:param name="p2" as="element()"/>
 <xsl:variable name="tt1" as="xs:boolean*">
  <xsl:sequence select="
  for $a in (true(),false()),$b in (true(),false()),$c in (true(),false())
  return
  f:eval($p1,$a,$b,$c)
  "/>
 </xsl:variable>
 <xsl:variable name="tt2" as="xs:boolean*">
  <xsl:sequence select="
  for $a in (true(),false()),$b in (true(),false()),$c in (true(),false())
  return
  f:eval($p2,$a,$b,$c)
  "/>
 </xsl:variable>
 <xsl:variable name="x" as="xs:boolean*">
  <xsl:for-each select="$tt1">
   <xsl:variable name="pn" select="position()"/>
   <xsl:sequence select="not(.) or $tt2[$pn]"/>
  </xsl:for-each>
 </xsl:variable>
 <xsl:sequence select="every $i in $x satisfies $i"/>
</xsl:function>

<xsl:function name="f:eval" as="xs:boolean">
 <xsl:param name="p" as="element()"/>
 <xsl:param name="a" as="xs:boolean"/>
 <xsl:param name="b" as="xs:boolean"/>
 <xsl:param name="c" as="xs:boolean"/>
 <xsl:choose>
  <xsl:when test="$p/self::item[.='A']">
   <xsl:sequence select="if($p/@required='true') then $a else not($a)"/>
  </xsl:when>
  <xsl:when test="$p/self::item[.='B']">
   <xsl:sequence select="if($p/@required='true') then $b else not($b)"/>
  </xsl:when>
  <xsl:when test="$p/self::item[.='C']">
   <xsl:sequence select="if($p/@required='true') then $c else not($c)"/>
  </xsl:when>
  <xsl:when test="$p/self::AND">
   <xsl:sequence select="f:eval($p/*[1],$a,$b,$c) and
f:eval($p/*[2],$a,$b,$c)"/>
  </xsl:when>
  <xsl:when test="$p/self::OR">
   <xsl:sequence select="f:eval($p/*[1],$a,$b,$c) or f:eval($p/*[2],$a,$b,$c)"/>
  </xsl:when>
  <xsl:otherwise>
   <xsl:sequence select="false()(:shouldn't happen:)"/>
  </xsl:otherwise>
 </xsl:choose>
</xsl:function>

</xsl:stylesheet>