Also:

- Remove the wp_strip_later hack.
- Let wp_lam, wp_rec, wp_... initiate the proof mode.

I also renamed `iProof` into `iStartProof`, as it is supposed to be
something internal, and not a substitute of Coq's `Proof` command (as
originally intended).

Fix a typo in constructions.tex

x_1 should be a_1

See merge request !35

Really, *all* of our files contain proof rules

Use agree instead of dec_agree

This demonstrates that a list-based agreement could work, and form an OFE. I didn't bother to prove all the functor laws.

Man, this reasoning with about the lists is annoying^^.

What I don't like about this is that un-injection (`agree_car`) is only non-expansive for valid elements. I want to try using a different equivalence relation, maybe I can find one where this works.

Cc @jjourdan @robbertkrebbers

See merge request !22

Thanks to Robbert for fixing gen_heap

State invariants in WP and the dead of heap_ctx.

This merge request changes the WP construction so that it takes _state interpretation_ as its parameter (part of the `irisG` type class), instead of building in the authoritative ownership of the entire state. When instantiating WP with a concrete language, one can choose the state interpretation. For example, for `heap_lang` we directly use `auth (gmap loc (frac * dec_agree val))`, and avoid the indirection through an invariant managing ownership of the entire state.

As a result, we no longer have to carry around `heap_ctx`.

See merge request !25

The WP construction now takes an invariant on states as a parameter
(part of the irisG class) and no longer builds in the authoritative
ownership of the entire state. When instantiating WP with a concrete
language on can choose its state invariant. For example, for heap_lang
we directly use `auth (gmap loc (frac * dec_agree val))`, and avoid
the indirection through invariants entirely.

As a result, we no longer have to carry `heap_ctx` around.

We typically use the _1 and _2 suffix to denote individual directions
of a lemmas that is a biimplication.