title: Type 'Object' is defined in an assembly that is not referenced (NET Standard 2.0/.NET Framework 4.6.1)
body: <p>I'm using the <a href="https://blogs.msdn.microsoft.com/dotnet/2017/05/10/announcing-net-core-2-0-preview-1/" rel="noreferrer">.NET Standard 2.0</a> preview, on which my Class Libraries are based.</p>
  
  <p>After having trouble with a few NuGet packages, especially regarding archive extraction, I decided to migrate my .NET Core 2.0 Console projects back to the .NET Framework 4.6.1.</p>
  
  <p>The .NET Framework 4.6.1 is supposed to implement the .NET Standard 2.0 specification - according to different sources. Especially the <a href="https://github.com/dotnet/standard/blob/master/docs/versions.md" rel="noreferrer">dotnet/standard GitHub Repo</a>.</p>
  
  <p><a href="https://i.stack.imgur.com/5eGO5m.png" rel="noreferrer"><img src="https://i.stack.imgur.com/5eGO5m.png" alt="Net Standard Implementation by Net Framework and Core"></a></p>
  
  <p>Unfortunately, the migration to the .NET Framework resulted in the following errrors throughout all of .NET Framework Console projects:</p>
  
  <blockquote>
    <p>Error CS0012  The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.</p>
  </blockquote>
  
  <p>Where <code>Object</code> can be anything: <code>Enum</code>, <code>Task</code>, ... </p>
  
  <p>How would I reference .NET Standard 2.0 class libraries with .NET Framework (4.6.1) without getting such errors?</p>