In my research article on kinds (and my dissertation), I have proved sufficient conditions for abstract interfaces to be sound. They are hard to explain, so I was looking for a simpler condition that implied the real one. I made a mistake in thinking that the locality restriction was a good candidate. But as Martin said, it is restrictive, and as Arjan shows it is not even safe! When I get the time, I will get back on this, implement a safe condition, and hopefully it will not be restrictive in practice.

-- DanielBonniot - 30 Apr 2003