You tell the guy he can claim sole authorship, but then you're disappointed when he doesn't share credit? Is that right?
No, not at all. I was disappointed because it was my idea for the book [nobody had thought of the idea at all] and I had handed him 1/3 of the book completed and he could not even say: "Thanks to ... ... who gave me some ideas for this book." Then he could be sole author and can reap the profit etc.
You have an idea for a chess book. It is an idea that nobody has ever tried. You gather material and start to write the book. However you become quite ill. You have the book 1/3 of the way completed but you do not know if you will ever recover from your illness. You are unable to finish but do not want to see your "idea" go to waste. The book would take about 6 months to finish.
So you contact another book author. You tell him your situation and about the book. You give him permission to complete the book and use all the writings and material you have already completed. You even tell him that he can designate himself as the sole author of the book and also he can keep all the profits from the book. He accepts and 7 months later--the book has been picked up by a chess book publisher and it is a very nice book and a success!
But he makes absolutely no mention of the work you have done so that the book will exist! No mention at all. What do you think?
PS I am never going to give out which book it is or who is the author.