title: uncheck a checkbox which is checked and freezed with a condition in Angular 5
body: <p>I have a table that iterates on JSON values, i have checkbox in the first column</p>
  
  <p>requirement: when 5 checkboxes are selected, the user shouldn't be able to select the 6th checkbox, but he can deselect any in the 5 checkboxes</p>
  
  <p>current scenario: i am able to freeze the checkboxes when the user selects 5 checkboxes but it isn't allowing me to deselect the selected checkbox </p>
  
  <pre><code>&lt;checkbox [forbidden]="isFull() &amp;&amp; !Selected" [ngModel]="Selected" (ngModelChange)="Change(Result, $event)"&gt;&lt;/checkbox&gt;
  </code></pre>
  
  <p>checkbox is a custom component in my code base</p>
  
  <pre><code>isFull() {
      return someService.Slots()===0; // availableSlots returns 5
  }
  
  Change(Result, $event){
      // some code irrelevant to the checkbox logic
      // Result holds the JSON value for iterating row
  }
  </code></pre>
  
  <p>Please provide a working plunker or any online editor for better understanding</p>
  
  <p>Thanks in advance</p>