excluding descendants (and all of their descendants as

How does one find all text elements that are descendants of the first para
element but exclude any text element that is a descendant of the second system
element?

<techinfo>
  <system>
    <descinfo>
      <para-seq>
        <para>
          <text>The quick brown fox jumped over the lazy systems
engineer.</text>
          <text>Hello world.</text>
          <style>
            <text>In the matter of Jardyce v. Jardyce:</text>
          </style>
          <system>
             <descinfo>
                 <para-seq>
                     <para>
                          <text>Blah, blah, blah...</text>
                           <text>more gibberish.</text>
                           <style>
                               <text>Nasty, Brutish, and Short Attorneys at
Law</text>
                           </style>
                        </para>
                      </para-seq>
                  </descinfo>
               </system>
            </para>
         </para-seq>
      </descinfo>
   </system>
</techinfo>

Thanks very much.