namespace Db4objects.Db4o { public interface IObjectContainer { System.Collections.IList Query (); System.Collections.Generic.IList Query (System.Collections.Generic.IList foo, System.Collections.Generic.IList bar); } } namespace Db4objects.Db4o.Internal { public abstract class ObjectContainerBase { public System.Collections.IList Query () { return null; } public System.Collections.Generic.IList Query(System.Collections.Generic.IList foo, System.Collections.Generic.IList bar) { return null; } } public abstract class ExternalObjectContainer : ObjectContainerBase, IObjectContainer { } class M { public static void Main () { } } }