title: all the checkboxes are getting checked on clicking a single checkbox
body: <p>i have a list of checkboxes in my angularjs code. when i click a checkbox, all the checkboxes get activated. How can i check only a single checkbox?</p>
  
  <p>here is my code</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.4.8/angular.min.js"&gt;&lt;/script&gt;
  &lt;body&gt;
  
  &lt;div ng-app="myApp" ng-controller="namesCtrl"&gt;
  
  &lt;p&gt;Type a letter in the input field:&lt;/p&gt;
  &lt;form action=""&gt;
  &lt;p&gt;&lt;input type="checkbox" ng-model="alpha" value="a"&gt;a&lt;/p&gt;
  &lt;p&gt;&lt;input type="checkbox" ng-model="alpha" value="b"&gt;b&lt;/p&gt;
  &lt;p&gt;&lt;input type="checkbox" ng-model="alpha" value="c"&gt;c&lt;/p&gt;
  &lt;p&gt;&lt;input type="checkbox" ng-model="alpha" value="d"&gt;d&lt;/p&gt;
  &lt;p&gt;&lt;input type="checkbox" ng-model="alpha" value="e"&gt;e&lt;/p&gt;
  &lt;p&gt;&lt;input type="checkbox" ng-model="alpha" value="f"&gt;f&lt;/p&gt;
  &lt;/form&gt;
  &lt;ul&gt;
    &lt;li ng-repeat="x in names | filter:alpha"&gt;
      {{ x }}
    &lt;/li&gt;
  &lt;/ul&gt;
  
  &lt;/div&gt;
  
  &lt;script&gt;
  angular.module('myApp', []).controller('namesCtrl', function($scope) {
      $scope.names = [
          'Jani',
          'Carl',
          'Margareth',
          'Hege',
          'Joe',
          'Gustav',
          'Birgit',
          'Mary',
          'Kai'
      ];
  });
  &lt;/script&gt;
  
  &lt;p&gt;The list will only consists of names matching the filter.&lt;/p&gt;
  
  
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>the code is working fine when i use radio buttons.. 
   this is the problem i'm facing</p>