title: jQuery: Test if checkbox is NOT checked
body: <p>I'm having trouble figuring this out. I have two checkboxes (in the future will have more):</p>
  
  <ul>
  <li><code>checkSurfaceEnvironment-1</code></li>
  <li><code>checkSurfaceEnvironment-2</code></li>
  </ul>
  
  <p>Basically, I want to write an if statement and test if one of them is checked and another is NOT checked. What's the easiest way to accomplish the following:</p>
  
  <pre class="lang-js prettyprint-override"><code>if ( $("#checkSurfaceEnvironment-1").attr('checked', true) &amp;&amp;
       $("#checkSurfaceEnvironment-2").is('**(NOT??)** :checked') ) {
          // do something
  }
  </code></pre>