IANAL, IANADD, but it's hard for me to imagine that there is any sensible or just way to resolve this other than to credit Karsten with a significant contribution to the Guide. Such a guide is of course largely factual and could bear many resemblances to Karsten's without constituting plagiarism or a violation of his copyright; but he presents strong evidence that the way this guide actually was written involved copying and adapting portions of his creative expression. "Plagiarism" would, I think, be too strong a word, and he is something less than a co-author of the Guide; but it seems reasonable for him to ask for some acknowledgment.
Cheers, - Michael
