title: Cannot write a value to a ko.computed unless you specify a 'write' option
body: <p>I am trying to use computed properties in another computed properties and when i run code i am getting following error in console. </p>
  
  <p><strong>Cannot write a value to a <code>ko.computed</code> unless you specify a 'write' option</strong></p>
  
  <pre><code>function AppViewModel() {
      var self = this; 
      self.firstName = ko.observable('rahul');
      self.lastName = ko.observable('sharma');
      self.fullName = ko.computed(function() {
        return self.firstName() +' ' + self.lastName();
      });
      self.upperFullName = ko.computed(function() {
        return self.fullName.toUpperCase();
      });  
  }
  // Activates knockout.js
  ko.applyBindings(new AppViewModel()); 
  </code></pre>
  
  <p>and here is html code and <a href="http://jsfiddle.net/rahularyansharma/PSajG/">js fiddle link</a> </p>
  
  <pre><code>&lt;p&gt;&lt;input data-bind="value: firstName"&gt;&lt;/p&gt;
  
  &lt;p&gt;&lt;input data-bind="value: lastName"&gt;&lt;/p&gt;
  
  &lt;p&gt;&lt;input data-bind="value: fullName"&gt;&lt;/p&gt;
  
  &lt;p&gt; &lt;span data-bind="text: upperFullName"&gt; &lt;/span&gt; &lt;/p&gt;
  </code></pre>