In the book, he makes no claim of ownership over the concept, he explains it is not his original idea and then goes on to apply the concept to the topic in hand. I am grateful that he took the time to propagate this idea in my direction. Paul, who is that ‘someone’ you refer to? Because, as a reader of his book, I believe he behaved perfectly ethically and honourably.

This seems to be a very ancient idea, I’m not sure it belongs to any one person in modern times!
David has been using it for many years; I have it in a collection of ideas clipped from his website 20 yrs ago.