title: tool for testing logic expressions
body: <p>can anyone recommend software (preferably for mac) or a web based tool, that can be used to evaluate logic expressions?</p>
  
  <p>For example I would like to be able to quickly test whether two expressions like:</p>
  
  <pre><code>$a = 'foo';
  $b = 'bar';
  $c = 'foo';
  
  ( !(($a == $c) &amp;&amp; ($b == $c)) )
  
  // and
  
  ( ($a != $c) || ($b != c$) )
  </code></pre>
  
  <p>are interchangeable or not.</p>
  
  <p>And also, is there generally an agreed upon best practice in relation to how to construct such expressions? For example to try to minimize the use of the negation, the order of the elements or something like that?</p>
  
  <p>Sometimes I find myself struggling a bit with these things :)</p>