Maciej - I need to think deeply about some of the things that have been pointed out. At the moment (this week) there's a project I want to progress a bit so won't be able to do that just yet. One thing I might do immmediately is to do something about that conversion operator. I think it's causing some problems with the stream operators, just for starters. You sometimes get ambiguities in certain contexts and, as you said, these operators can do that. I have a fix, but am not totally satisfied. I've attached the "fixed" version. The comment at the top has also been corrected. Nice to have comments that don't tell porkies.