A semantic cut admissibility proof for the logic of Bunched Implications and extensions. See the preprint.

Intro

We formalize the sequent calculus of BI and give an algebraic proof of cut admissibility. We parametrize the calculus by an arbitrary collection of "simple structural rules" (see theories/seqcalc.v for the definition).

Structure (in the theories directory):

• syntax.v, terms.v -- formulas of BI and "bunched terms". A bunched term is essential a formula built up only from ∗/, and ∧/; and variables.
• interp.v -- interpretation of formulas and bunched terms in a BI algebra
• seqcalc.v -- sequent calculus + soundness
• bunch_decomp.v -- helpful lemmas about decompositions of bunches
• seqcalc_height.v -- the same sequent calculus, but with the notion of proof height. Includes proofs of invertibility of some of the rules.
• algebra/bi.v, algebra/interface.v -- BI algebras
• algebra/from_closure.v -- BI algebra from a closure operator
• cutelim.v -- the universal model for cut elimination

There is also a formalization of the same method but for BI with an S4-like box modality. See seqcalc_s4.v, seqcalc_height_s4.v, interp_s4.v, and cutelim_s4.v in the theories folder.

Compilation

You will need a copy of std++ installed. You can install the dependency with opam using opam install --deps-only . or the whole developement with opam install .

If you have std++ installed then you can compile the project with make -jN where N is the number of threads you want to use. Compile the HTML docs with make html.

Copyright

The Coq formalization is distributed under the BSD-3 licence. Some code was adapted from the Iris project https://iris-project.org.