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    Iris 3.0: invariants and weakest preconditions encoded in the logic. · 1f589858
    Robbert Krebbers authored
    This commit features:
    - A simpler model. The recursive domain equation no longer involves a triple
      containing invariants, physical state and ghost state, but just ghost state.
      Invariants and physical state are encoded using (higher-order) ghost state.
    - (Primitive) view shifts are formalized in the logic and all properties about
      it are proven in the logic instead of the model. Instead, the core logic
      features only a notion of raw view shifts which internalizing performing frame
      preserving updates.
    - A better behaved notion of mask changing view shifts. In particular, we no
      longer have side-conditions on transitivity of view shifts, and we have a
      rule for introduction of mask changing view shifts |={E1,E2}=> P with
      E2 ⊆ E1 which allows to postpone performing a view shift.
    - The weakest precondition connective is formalized in the logic using Banach's
      fixpoint. All properties about the connective are proven in the logic instead
      of directly in the model.
    - Adequacy is proven in the logic and uses a primitive form of adequacy for
      uPred that only involves raw views shifts and laters.
    Some remarks:
    - I have removed binary view shifts. I did not see a way to describe all rules
      of the new mask changing view shifts using those.
    - There is no longer the need for the notion of "frame shifting assertions" and
      these are thus removed. The rules for Hoare triples are thus also stated in
      terms of primitive view shifts.
    - Maybe rename primitive view shift into something more sensible
    - Figure out a way to deal with closed proofs (see the commented out stuff in
      tests/heap_lang and tests/barrier_client).