title: prometheus rule: check for expression value in range
body: <p>In a prometheus alert rule, how do I check for a value to be in a certain range? </p>
  
  <pre><code>for eg., (x &gt; 80 &amp;&amp; x &lt;= 100); 
  </code></pre>
  
  <p>when x is a complex expression it feels unnecessary to evaluate it twice. is there another way to represent this expression?</p>