title: C# .NET Rx- Where is System.Reactive?
body: <p>I have an intensive Java background so forgive me if I'm overlooking something obvious in C#, but my research is getting me nowhere. I am trying to use the reactive Rx .NET library. The compiler is not complaining about the <code>IObservable</code> but it is with the call to the <code>zip</code> method. It is throwing the "... are you missing a using directive or assembly reference?" </p>
  
  <p>I've been going through the namespaces and I cannot find what is looking for. I cannot find the <code>System.Reactive</code> which also throws an error if used, and all the references are already included for this Windows 8.1 app. Can someone please give me a lead on what is wrong?</p>
  
  <pre><code>public sealed class EventEngine
  {    
      private static readonly EventEngine singleton = new EventEngine();
  
      public static EventEngine get()
      {
          return singleton;
      }
  
      public IObservable&lt;MusicNote&gt; CurrentKey { get; set; }
      public IObservable&lt;Scale&gt; CurrentScale { get; set; }
  
      public IObservable&lt;AppliedScale&gt; CurrentAppliedScale
      {
          get
          {
              return CurrentScale.zip(CurrentKey,
                  (s, k) =&gt; AppliedScale.getAppliedScale(k, s));
          } 
      }
  
      private EventEngine() {}
  }
  </code></pre>
  
  <p><strong>*UPDATE *</strong></p>
  
  <p>Here is the working version after considering input from answers. </p>
  
  <pre><code>public sealed class EventEngine
  {
      private static readonly EventEngine singleton = new EventEngine();
  
      public static EventEngine get()
      {
          return singleton;
      }
  
      public IObservable&lt;MusicNote&gt; CurrentKey { get; set; }
      public IObservable&lt;Scale&gt; CurrentScale { get; set; }
  
      public IObservable&lt;AppliedScale&gt; CurrentAppliedScale
      {
          get
          {
              return Observable.Zip(CurrentScale, CurrentKey,
                  (s, k) =&gt; AppliedScale.getAppliedScale(s,k));
          } 
      }
  
      private EventEngine() {}
  }
  </code></pre>