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Since functor instances are just used as combinators, there is really
no need for functors that are not contractive.

make the global functor stuff in the various constructions more uniform; change it such that barrier/proof does not have to repeat the functors it needs

This cleans up some ad-hoc stuff and prepares for a generalization
of saved propositions.

I made the list of iFunctors monomorphic to avoid having to deal with
universe polymorphism, that is still somewhat flaky.