title: How do you convert strings (Logical Operations & Relational Operations) to symbolic objects?
body: <p>How do you convert strings (Logical Operations &amp; Relational Operations) to symbolic objects? For example..</p>
  
  <pre><code>zz = '(xx&gt;=-4 ) &amp; (xx&lt;-3 )'
  </code></pre>
  
  <p>How do you convert <code>zz</code> to a symbolic object?</p>