title: Allow checking to a checkbox even after adding attr("checked", false)
body: <p>I am not sure if a formulated the title correctly but the logic is this. <br/><br/>
  I have 4 checkboxes, <strong>3 Yes</strong> and <em>1 No</em>. Selecting 3 <strong>Yes</strong> will uncheck <em>No</em> and selecting <em>No</em> will uncheck <strong>Yes</strong>.<br/><br/>
  My jQuery as per below:<br/><br/></p>
  
  <pre><code>var yes = $("input[type=checkbox].yes");
  
  if (yes.length == yes.filter(":checked").length) {
      $("#no").attr("checked", false);
  } else if($("#no").is(":checked")) {
      yes.attr("checked", false);
  } else {
      // do nothing
  }
  </code></pre>
  
  <p><br/><br/>
  It works. However, if I checked all <strong>Yes</strong>, I won't be able to select <em>No</em>. Instead, I need to uncheck 1 <strong>Yes</strong> to select <em>No</em>. Same thing for <em>No</em>. If I check <em>No</em>, all <strong>Yes</strong> will be unchecked. However I need to uncheck <em>No</em> to be able to select <strong>Yes</strong> again.<br/><br/>
  Will there be a way that I can still select <em>No</em> if all <strong>Yes</strong> is checked?
  <br/><br/>
  Thanks!</p>
  
  <p><strong>UPDATE</strong><br/>
  Including HTML now <br/><br/></p>
  
  <pre><code>&lt;form id="checkbox-testing" &gt;
  &lt;div class="checkform"&gt;
      &lt;label&gt;                        
        &lt;input class="yes" type="checkbox" value="Yes, 1" id="yes1"&gt;&lt;span&gt;&amp;nbsp;Yes, 1&lt;/span&gt; 
      &lt;/label&gt;
      &lt;label&gt;                        
        &lt;input class="yes" type="checkbox" value="Yes, 2" id="yes2"&gt;&lt;span&gt;&amp;nbsp;Yes, 2&lt;/span&gt;
      &lt;/label&gt;
      &lt;label&gt;                        
        &lt;input class="yes" type="checkbox" value="Yes, 3" id="yes3"&gt;&lt;span&gt;&amp;nbsp;Yes, 3&lt;/span&gt;
      &lt;/label&gt;
      &lt;label&gt;                        
        &lt;input type="checkbox" value="No" id="no"&gt;&lt;span&gt;&amp;nbsp;No&lt;/span&gt;
      &lt;/label&gt;
  &lt;/div&gt;
  &lt;input type="submit" value="Test" /&gt;
  &lt;/form&gt;
  </code></pre>