Hi Ingo, thank you so much for your much appreciated input and your findings.
This gives me enough stuff to dig into for the next few days - from a first read it's very interesting! I'll come back to you as soon as I am one step further. Regarding "jaap", the only "Jaap" that came to my mind in an instant was Jaap Vermeulen. He once worked at Sequent and his name turned up here and there in some sources and files over the years. But, again, this is just a guess, but it's maybe worth asking him directly. For the CD set: If it was already offered about a decade ago, I am quite sure that I have it somewhere - if not I am confusing it with some other CD set. However, the cover looked immediately familiar. Regards, Ralph (the one half)
