Athena Proof Framework

This repo contains the source code for Athena, a system for proof engineering based on polymorphic multi-sorted first-order logic.

Athena supports natural deduction, proof organization and abstraction, theory development, equational reasoning and (conditional) rewriting, structural induction, and more. It is also seamlessly integrated with a number of automated theorem provers, as well as SAT and SMT solvers.

A Quick Example

Athena is very close in style to the way humans naturally perform deduction.

Below is a simple example of proving the asymmetry of the < (less-than) relation, taken verbatim from the Athena book:

module Asymmetry {
  domain D
  declare <: [D D] -> Boolean

  define [x y z] := [?x:D ?y:D ?z:D]

  assert* irreflexivity := (~ x < x)
  assert* transitivity := (x < y & y < z ==> x < z)

  conclude asymmetry := (forall x y . x < y ==> ~ y < x)
    pick-any a:D b:D
      assume (a < b)
        (!by-contradiction (~ b < a)
          assume (b < a) 
            let {less := (!chain-> [(b < a) 
                                ==> (a < b & b < a)    [augment]
                                ==> (a < a)            [transitivity]]);
                 not-less := (!chain-> [true 
                                    ==> (~ a < a)      [irreflexivity]])}
              (!absurd less not-less))

} 

Quickstart

Follow the setup instructions for Athena on the repo's wiki. Below are some quick setup instructions if you're on a Linux machine.

To start using Athena right away, simply download and unpack the latest release. After doing so, ensure that the ATHENA_HOME environment variable is set to the path to the files.

After expanding the packaged release, the contents of the athena-[platform]-[version] directory should look like this

tannr@pop-os: ~/athena-linux-v1.4.1$ ls ./

athena*  build_logs.txt  lib/  util/

It is recommended to also add Athena to your $PATH for convenience.

Some features and tests may require an external automated theorem prover and/or SAT solver. The defaults are SPASS and Minisat. These tools are not shipped with Athena, so must be installed independently if they are needed (you will need them, for example, if you intend on using the sat or prove functions within an Athena project).

For Windows users

If you are on Windows, it is recommended to use WSL, which will allow you to use the packaged release of Athena for linux platforms.

Building From Source

For build instructions, please refer to the Building Athena page in the wiki.

Codebase Structure

Athena is implemented in SML. At its present state, that implementation comprises 80 files, listed in sources.cm.

There are some resources in the repo that specify the dependencies between the various source files:

• file_dependencies.yaml lists all the files that each source file depends on.

• structure_dependencies.yaml lists all the (SML) structures defined in the code base, and for each structure S,
  it lists all structures on which S depends.

• dependency_graph.pdf is a graph (that can be viewed with any pdf reader, e.g., using a browser), which depicts these dependencies graphically.

Note that athena.sml is at the top of the graph (it's essentially the 'main' file of the project), while base.sml is at the bottom.

Regression testing

Run python3 tests/regression/regressionTest.py. The function runAthenaTests will return 0 if all the tests pass and some positive integer
less than 125 otherwise. Thus, this function can be used with git bisect, which is useful in debugging a range of commits. By default,
the script runs with a heap image produced by smlnj as described above, but you can also pass it (as the first argument) the name of an
executable produced by MLton (these executables tend to be faster than the heap images produced by smlnj),
e.g., python3 tests/regression/regressionTest.py './athena'.

Learn Athena

The most thorough resource for learning to use Athena is the book, Fundamental Proof Methods in Computer Science or FPMICS, authored by Konstantine Arkoudas and David Musser.

Examples of Athena can also be found in the tests/regression/ directory, including all of the code examples provided with the book.

Other tutorials and online courses are undergoing active development.

History of Athena

Athena was developed by Konstantine Arkoudas, roughly between 2000 and 2015. The core of the language had more or less settled by 2004, but there were a number of subsequent changes and extensions, some of them conceived and implemented after 2010, such as modules, a good deal of infix syntax, proof chaining (implemented via the primitive 'chain' procedure, both for equations and for logical implications/equivalences), integration with SMT solvers and tabled Prolog systems such as XSB, and others.

In early 2022, Tannr Allard - a long time Athena user - formed the Athena Foundation, a non-profit organization dedicated to the maintenance and continued development of the Athena language. Tannr is now the core maintainer of the Athena language & regularly collaborates with Konstantine, who serves as a board member & expert advisor in the Athena Foundation.