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The performance gain seems neglectable, unfortunatelly...

This better seals off their definition. Although it did not give
much of a speedup, I think it is conceptually nicer.

This avoids ambiguity with P and Q that we were using before for both
uPreds/iProps and indexed uPreds/iProps.

It is doing much more than just dealing with ∈, it solves all kinds
of goals involving set operations (including ≡ and ⊆).

Also, make our redefinition of done more robust under different
orders of Importing modules.

The rationale is that, just like the always lemmas about uPred and the frame-preserving updates for maps and iprdos, the versions with the ' are the "more specific" versions, hard-coding more assumptions in the shape of their conclusion.

Also do some minor clean up.

This way we avoid many one-off indexes and no longer need special cases for
index 0 in many definitions. For example, the definition of the distance
relation on option and excl has become much easier. Also, uPreds no longer need
to hold at index 0.

In order to make this change possible, we had to change the notions of
"contractive functions" and "chains" slightly.

Thanks to Aleš Bizjak and Amin Timany for suggesting this change and to help
with the proofs.

Actual proofs will end up using own and inv, and none of the notions defined in ownership.v

No idea why these aren't resolved automatically, for unary predicates
they do not seem necesarry.

...unfortunately, that proof actually got longer because some automation no longer works

This way we can more easily state lemmas for concrete languages for
arbitrary global functors.

The proofs are neither short nor nice, but at least they compile
fast (4 sec for the whole file) and the statements look like
they would look like on paper.