A tactic for deciding Kleene algebras
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README.md

ATBR

Travis Contributing Code of Conduct Gitter

This library provides algebraic tools for working with binary relations. The main tactic provided is a reflexive tactic for solving (in)equations in an arbitrary Kleene algebra. The decision procedure goes through standard finite automata constructions.

The design and implementation of the library is described in the paper Deciding Kleene Algebras in Coq (DOI:10.2168/LMCS-8(1:16)2012).

Note that the initial authors consider this library to be superseded by the Relation Algebra library, which is based on derivatives rather than automata.

Meta

  • Author(s):
    • Thomas Braibant (initial)
    • Damien Pous (initial)
  • Coq-community maintainer(s):
  • License: GNU Lesser General Public License v3.0 or later
  • Compatible Coq versions: Coq master (use the corresponding branch or release for other Coq versions)
  • Compatible OCaml versions: all versions supported by Coq
  • Additional dependencies: none

Building and installation instructions

The easiest way to install the latest released version is via OPAM:

opam repo add coq-released https://coq.inria.fr/opam/released
opam install coq-atbr

To instead build and install manually, do:

git clone https://github.com/coq-community/atbr
cd atbr
make   # or make -j <number-of-cores-on-your-machine>
make install

After installation, the included modules are available under the ATBR namespace.

Documentation

Here is a succinct description of each file. The user can also refer to files Examples.v and ChurchRosser.v.

Library files

Filename Description
ATBR Export all relevant modules, except those related to matrices
ATBR_Matrices Export all relevant modules, including those related to matrices

Algebraic hierarchy

Filename Description
Classes Definitions of algebraic classes of the development
Graph Lemmas and hints about the base class (carrier with equality)
Monoid Monoids, free monoids, finite iterations over a monoid, various tactics
SemiLattice Semilattices, tactics: normalise, reflexivity, rewrite
SemiRing Idempotent semirings, tactics: normalise, reflexivity, rewrite
KleeneAlgebra Kleene algebras, basic properties
Converse Structures with converse (semirings and Kleene Algebras)
Functors Functors between the various algebraic structures
StrictKleeneAlgebra Class of Strict Kleene algebras (without 0), and extension of the decision procedure

Models

Filename Description
Model_Relations Kleene Algebra of (heterogeneous) binary relations
Model_StdRelations Kleene Algebra of standard (homogeneous) binary relations
Model_Languages Kleene Algebra of languages
Model_RegExp Kleene Algebra of regular expressions (syntactic free model), typed reification
Model_MinMax (min,+) Kleene Algebra (matrices on this algebra give weighted graphs)

Matrices

Filename Description
MxGraph Matrices without operations; blocks definitions
MxSemiLattice Semilattices of matrices
MxSemiRing Semiring of matrices
MxKleeneAlgebra Kleene algebra of matrices (definition of the star operation)
MxFunctors Extension of functors to matrices

Decision procedure for KA

Filename Description
DKA_Definitions Base definitions for the decision procedure for KA (automata types, notations, ...)
DKA_StateSetSets Properties about sets of sets
DKA_CheckLabels Algorithm to check whether two regex have the same set of labels
DKA_Construction Construction algorithm, and proof of correctness
DKA_Epsilon Removal of epsilon transitions, proof of correctness
DKA_Determinisation Determinisation algorithm, proof of correctness
DKA_Merge Union of DFAs, proof of correctness
DKA_DFA_Language Language recognised by a DFA, equivalence with the evaluation of the DFA
DKA_DFA_Equiv Equivalence check for DFAs, proof of correctness
DecideKleeneAlgebra Kozen's initiality proof, kleene_reflexivity tactic

Other tools

Filename Description
StrictStarForm Conversion of regular expressions into strict star form, kleene_ssf tactic
Equivalence Tactic for solving equivalences by transitivity

Examples

Filename Description
Examples Small tutorial file, that goes through our set of tactics
ChurchRosser Simple usages of kleene_reflexivity to prove commutation properties
ChurchRosser_Points Comparison between a standard CR proof and algebraic ones

Misc.

Filename Description
Common Shared simple tactics and definitions
BoolView View mechanism for Boolean computations
Numbers NUM interface, to abstract over the representation of numbers, sets, and maps
Utils_WF Utilities about well-founded relations; partial fixpoint operators (powerfix)
DisjointSets Efficient implementation of a disjoint sets data structure
Force Functional memoisation (in case one needs efficient matrix computations)
Reification Reified syntax for the various algebraic structures

Finite sets and maps

Filename Description
MyFSets Efficient ordered datatypes constructions (for FSets functors)
MyFSetProperties Handler for FSet properties
MyFMapProperties Handler for FMap properties

OCaml modules

Filename Description
reification.ml reification for the reflexive tactics

Tactics

Reflexive tactics

Tactic Description
semiring_reflexivity solve an (in)equation on the idempotent semiring (*,+,1,0)
semiring_normalize simplify an (in)equation on the idempotent semiring (*,+,1,0)
semiring_clean simplify 0 and 1
semiring_cleanassoc simplify 0 and 1, normalize the parentheses
kleene_reflexivity solve an (in)equation in Kleene Algebras
ckleene_reflexivity solve an (in)equation in Kleene Algebras with converse
skleene_reflexivity solve an (in)equation in Strict Kleene Algebras (without 0)
kleene_clean_zero remove zeros in a KA expression
kleene_ssf put KA expressions into strict star form

Rewriting tactics

Tactic Description
ac_rewrite H rewrite a closed equality modulo (AC) of (+)
monoid_rewrite H rewrite a closed equality modulo (A) of (*)

Other tactics

Tactic Description
converse_down push converses down to terms leaves
switch add converses to the goal and push them down to terms leaves

Acknowledgements

The initial authors would like to thank Guilhem Moulin and Sebastien Briais, who participated to a preliminary version of this project. They are also grateful to Assia Mahboubi, Matthieu Sozeau, Bruno Barras, and Hugo Herbelin for highly stimulating discussions, as well as numerous hints for solving various problems.