title: XPATH find a node if no other node has a sertin value
body: <p>i need to return all of the book only if ther is no book with the price of 14.95.... </p>
  
  <p>the DTD</p>
  
  <pre><code>&lt;!ELEMENT inventory (book)+&gt;
  &lt;!ELEMENT book (title, author+, publisher+, price, chapter*)&gt;
  &lt;!ATTLIST book num ID #REQUIRED&gt;
  &lt;!ELEMENT chapter (title, (paragraph* | section*))&gt;
  &lt;!ELEMENT section (title?, paragraph*)&gt;
  &lt;!ELEMENT title (#PCDATA)&gt;
  &lt;!ELEMENT author (#PCDATA)&gt;
  &lt;!ELEMENT publisher (#PCDATA)&gt;
  &lt;!ELEMENT price (#PCDATA)&gt;
  &lt;!ATTLIST price currency CDATA #FIXED "usd"&gt;
  &lt;!ELEMENT paragraph (#PCDATA | emph | image)*&gt;
  &lt;!ELEMENT emph (#PCDATA)&gt;
  &lt;!ELEMENT image EMPTY &gt;
  &lt;!ATTLIST image
            file
            CDATA #REQUIRED
            height CDATA #IMPLIED
            width CDATA #IMPLIED &gt;
  </code></pre>
  
  <p>xml for example the xml is not constraint to be this one</p>
  
  <pre><code>version="1.0" encoding="UTF-8"?&gt;
  &lt;!DOCTYPE inventory SYSTEM "books.dtd"&gt;
     &lt;inventory&gt;
        &lt;book num="b1"&gt;
           &lt;title&gt;Snow Crash&lt;/title&gt;
           &lt;author&gt;Neal Stephenson&lt;/author&gt;
           &lt;publisher&gt;Spectra&lt;/publisher&gt;
           &lt;price&gt;14.95&lt;/price&gt;
           &lt;chapter&gt;
           &lt;title&gt;Snow Crash - Chapter A&lt;/title&gt;
           &lt;paragraph&gt;
              This is the
              &lt;emph&gt;first&lt;/emph&gt;
              paragraph.
              &lt;image file="firstParaImage.gif"/&gt;
              After image...
           &lt;/paragraph&gt;
           &lt;paragraph&gt;
              This is the
              &lt;emph&gt;second&lt;/emph&gt;
              paragraph.
              &lt;image file="secondParaImage.gif"/&gt;
              After image...
           &lt;/paragraph&gt;
        &lt;/section&gt;
     &lt;/chapter&gt;
  &lt;/book&gt;
  &lt;book num="b3"&gt;
     &lt;title&gt;Zodiac&lt;/title&gt;
     &lt;author&gt;Neal Stephenson&lt;/author&gt;
     &lt;publisher&gt;Spectra&lt;/publisher&gt;
     &lt;price&gt;7.50&lt;/price&gt;
     &lt;chapter&gt;
        &lt;title&gt;Zodiac - Chapter A&lt;/title&gt;
     &lt;/chapter&gt;
  &lt;/book&gt;
  &lt;/inventory&gt;
  </code></pre>
  
  <p>i konw how to find all of the book with price difrent from 14.95.. but i dont now how to do the if statment in XPTH
  the assigment is in XPTH only</p>