title: Knockout js: Bind checkbox enable when boolean is false
body: <p>Each of my elements has IsAnabled and IsDeafult. If IsDefault = true, then the checkbox should be disabled. </p>
  
  <p>When I do like this it works, except I want the oppsite effect for "enable":</p>
  
  <pre><code>&lt;input type="checkbox" data-bind="checked: IsEnabled, enable: IsDefault" /&gt;
  </code></pre>
  
  <p>I have tried:</p>
  
  <pre><code>&lt;input type="checkbox" data-bind="checked: IsEnabled, enable: !IsDefault" /&gt;
  &lt;input type="checkbox" data-bind="checked: IsEnabled, enable: IsDefault == 'false'" /&gt;
  &lt;input type="checkbox" data-bind="checked: IsEnabled, enable: IsDefault != 'true'" /&gt;
  &lt;input type="checkbox" data-bind="checked: IsEnabled, enable: IsDefault != true" /&gt;
  &lt;input type="checkbox" data-bind="checked: IsEnabled, enable: IsDefault == '0'" /&gt;
  </code></pre>
  
  <p>but still no luck... </p>