title: pre-release Collections.Immutable
body: <p>Has anyone succeeded in opening the pre-release <code>System.Collections.Immutable</code> from NuGet in F#?</p>
  
  <p>I'm getting this error:</p>
  
  <blockquote>
    <p>The type 'IEnumerable`1' is required here and is unavailable. You must add a reference to assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.</p>
  </blockquote>
  
  <p>Even though my project is .NET 4.5</p>
  
  <p>Tried explicitly opening System.Runtime and that did not work either. I am referencing <code>.NETCore\v4.5\System.Runtime.dll</code></p>