So you are planning not to prove try_unwrap nor any of the the Weak business?

Hum, sorry, it seems like you will be indeed able to do try_unwrap. Will this work for get_mut? That seems quite subtle, there are plenty of things to do when closing back the borrow, but that should work ;)

Well, except that you forgot to put in the invariant the updates used for ending ν and inheriting the ownership of the content.

Right, I did not plan to support weak counts, at least in the beginning. I guess I'll see for the rest.^^ Indeed I forgot to put the lifetime end thing somewhere.