Re: As I wrote about something else a month or so ago ...
"The legalistic definition of Unix would exclude research Unixes though, so how good a definition is it really?"
Ah. I see where you are going now.
Linux, BSD, Apple's Darwin-based contributions, Android and ChromeOS are all Unix in scope and feel.
What they are not is examples of UNIX[tm], unless they have paid to use that trademark.
Kind of like the definition of "organic" food, which means the farmer has paid a state agency a fee to verify that said food was grown to a certain standard. Personally, I refuse to pay that rather high fee (which I would have to pass on to my customers), so I can't sell it as "Organic", even though it is, in fact, grown to that exact same standard (some would say better, actually).
However, there is nothing stopping me from marketing it as "organically grown".
UNIX[tm] is "Organic" ... Unix is organically grown. Two like products, one of which has paid money for an additional virtually meaningless tag ... the cost of which needs to be passed along to the consumer.