We no longer abuse empty strings for anonymous binders. Instead, we
now have a data type for binders: a binder is either named or
anonymous.

It is based on type classes and can it be tuned by providing
instances, for example, instances can be provided to mark that
certain expressions are closed.

Also, use "set_solver by tac" to specify a tactic.

I am now also using reification to obtain the indexes corresponding to
the stuff we want to cancel instead of relying on matching using Ltac.

barrier: strive for consistency between barrierGF and the inGF assumptions; also change some instance names

And now the part that I forgot to commit.

Also, give all these global functors the suffix GF to avoid shadowing
such as we had with authF.

And add some type annotations for clarity.

due to an accidental git commit --amend after a git push.

This strengthens some lemmas that are written using the notion of closednes, shortening some proofs all the way up to barrier.v

This is still a rather horrible proof, though. More work to be done.

this makes it slightlymore annoying to use because we have to elliminate the box. one more reason to have a proof mode ;-)