title: Xamarin - Multi-targetting - "'System.ValueTuple`2' is declared in multiple referenced"
body: <p>As soon as I try to compile code that use C# 7 tuples with multi targets (<code>netstandard2.0</code> and <code>xamarin.iOS</code>) I got the following error:</p>
  
  <blockquote>
    <p>Predefined type 'System.ValueTuple`2' is declared in multiple
    referenced assemblies</p>
  </blockquote>