New answers tagged books-generally
There are a number of works about Acher, from the historical-fiction to the scholarly and Hebrew. In addition to the books I mentioned in the comments above, various books by Robert Chazan discuss the medieval figures you mention.
There is a new book that is quite well written especially for a former Skver Chossid. It is his own memoir of his journey to apostasy but you might find it useful. All Who Go Do Not Return by Shulem Deen.
[excuse my English, I am not native to it] According to the Halacha, any detail agreed upon in advance (as in this case) by both sides, is legally binding. This of course unless it contradicts the laws of the Tora (which it does not).
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