Okay.
Interoperability is not really an industry issue, in many ways. The first way we look at it is of course with regard to standards, and that is something we work on. Even then, we frequently don't actually apply NATO standards. We create our own. So standards is a good, okay word, but I'm not entirely convinced in my own mind that it's the right way to go...or not the right way to go; I don't think it's the whole answer to the question.
I think interoperability is something that the agencies try really hard to achieve in the NATO environment. I think at the national level, it's the procurement executive who does interoperability more than it is industry. Although, of course, industry will say we're fully interoperable, actually it's government demand more than it is an industry output.
I'm not really prepared to comment on the S-400, I'm afraid. That is way beyond my pay grade. It's entirely up to Turkey.