An anecdote: sometime fairly early after the Mark Williams company started offering their Coherent system (a Unix clone), some AT&T legal people asked me to visit Mark Williams for purposes of determining whether what they were offering was a rip-off (i.e. essentially a copy) of the currently licensed Unix done by us. I find it hard to reconstruct the date this happened, but it was a long time ago; probably early 1980s. I went to Chicago with Otis Wilson, who was then involved in Unix licensing. It was a rather strange experience. The Mark Williams company was a paint producer, and I was given to understand that the subsidiary that was doing Coherent was, approximately, a corporation arranged by a father who, approaching retirement, had more or less shut down the older business and was using the corporate name and legal setup to help his son in a new venture. Otis and I visited the offices of Mark Williams on the outskirts of Chicago and were received with courtesy and some deference. We talked to the father and the son (Bob Swartz, i.e. the guy behind Coherent). There had been communication before, and from their point of view we were like the IRS auditors coming in. From my point of view, I felt the same, except that playing that role was a new, and not particularly welcome, experience. The locale of the company was in an industrial section and it definitely retained the flavor of a the offices of a paint company being recycled. What I actually did was to play around with Coherent and look for peculiarities, bugs, etc. that I knew about in the Unix distributions of the time. Whatever legal stuff had been talked about in the letters between MWC and AT&T didn't allow us to look at their source. I'd made some notes about things to look for. I concluded two things: First, that it was very hard to believe that Coherent and its basic applications were not created without considerable study of the OS code and details of its applications. Second, that looking at various corners convinced me that I couldn't find anything that was copied. It might have been that some parts were written with our source nearby, but at least the effort had been made to rewrite. If it came to it, I could never honestly testify that my opinion was that what they generated was irreproducible from the manual. I wrote up a detailed description of this. I can't find it, probably because at the time I was advised that it was privileged lawyer/client material. Partly at the time, partly thereafter, I learned that a variety of Unix enthusiasts (several from U. Toronto) had spent time there. In the event, "we" (=AT&T) backed off, possibly after other thinking and investigation that I'd wasn't involved in. So far as I know, after that MWC and Coherent were free to offer their system and allow it to succeed or fail in the market. I suppose there's a second story about the suit by USL against BSDI and then UCB, but my own involvement was far tinier and didn't get me a trip to Falls Church or Berkeley to snoop. What advice I offered in this situation was exactly in line with that about MWC/Coherent, and as it turned out the resolution (though more costly for all) was pretty much the same. (As a capper, Bob Swartz came by Bell Labs a week or so ago, and we had a pleasant social visit.) Dennis