namespace A

{

    class FooAttribute : System.Attribute

    {

    }

}

namespace B

{

    class FooAttribute : System.Attribute

    {

    }

}

​

namespace C

{

    class Foo : System.Attribute

    {

    }

}

​

namespace D

{

    using A;

    using B;

    using C;

    [Foo]

    class Bar 

    {

    }

}

​

public class Program

{

    public static void Main()

    {

    }

}