Compiler Error CS0528

'interface' is already listed in interface list

An interface-inheritance list includes a duplicate. An interface can only be specified once in the inheritance list.

The following sample generates CS0528:

// CS0528.cs
namespace x
{
   public interface a
   {
   }

   public class b : a, a   // CS0528
   {
      public void Main()
      {
      }
   }
}