Proving anything is going to be tough. If Obama and Ayers were that close, Ayers's phrases may have entered Obama's conversation and rough drafts without Ayers actually writing the book.
It's hard to prove ghost-writing, but the circumstantial evidence is strong. Obama has no history of high-quality writing other than the books that he wrote when he met Ayers. Even though Obama came from an island state and an island nation where you might expect a high amount of water exposure and experience, Obama has not offered up any history as a youth of engaging in boating, fishing, surfing, or any interest in the sea at all.
If, with that background, I'm asked to believe that he's exceptional in the use of nautical metaphors strictly from research alone, it's a leap that I need more convincing to take.
-PJ
It goes back to what I hinted at earlier, the use of shibboleths.
Writing about something that is so ingrained in one's culture and being, that it is almost an identifying trait, is something that stands apart from a description as a result of research.
The author of this article is setting up his separate points as shibboleths, things about this particular woman that are ingrained in her culture, her family, and her upbringing, backed up with circumstantial evidence including immersion in music, theater, and access to both across the street from her home.
Again, I am not a scholar in Shakespeare in any sense. I guess that frees me to be more accepting of the arguments made in this article.
-PJ