For "proof", you'll have to read Dr. Parmet's 1960 book on JFK which concludes that Sorenson wrote it and that while JFK contributed some notes with ideas for the book, Sorenson was its author. No, I wasn't in JFK's hospital room and I doubt you were either. The first time in history a Pulitzer Prize was awarded for a ghostwritten book.
I read the book years ago. It was good, but thinking back now, do you think it was Pulitzer Prize quality? I mean, how much money do you think changed hands under the table, to seal the award for JFK?
Don't knock JFKs Pulitzer. His daddy paid damn good money for it.