XForm - constraint based on answer of previous question

constraint

<?xml version="1.0"?>
<h:html xmlns="http://www.w3.org/2002/xforms" xmlns:ev="http://www.w3.org/2001/xml-events" xmlns:h="http://www.w3.org/1999/xhtml" xmlns:jr="http://openrosa.org/javarosa" xmlns:orx="http://openrosa.org/xforms/" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <h:head>
    <h:title>constraint</h:title>
    <model>
      <instance>
        <constraint id="constraint">
          <age/>
          <min_years_smoked/>
          <years_smoked/>
          <meta>
            <instanceID/>
          </meta>
        </constraint>
      </instance>
      <bind constraint=".&gt;= 12 and .&lt;=100" nodeset="/constraint/age" type="int"/>
      <bind calculate=" /constraint/age  - 12" nodeset="/constraint/min_years_smoked" type="string"/>
      <bind constraint=".&lt;=  /constraint/min_years_smoked  and .&lt;= 65" nodeset="/constraint/years_smoked" type="int"/>
      <bind calculate="concat('uuid:', uuid())" nodeset="/constraint/meta/instanceID" readonly="true()" type="string"/>
    </model>
  </h:head>
  <h:body>
    <input ref="/constraint/age">
      <label>How old are you?</label>
    </input>
    <input ref="/constraint/years_smoked">
      <label>How many years have you smoked</label>
    </input>
  </h:body>
</h:html>