This code interfaces HOL Light to the MiniSat propositional prover, so
that the proof logs produced by MiniSat can be turned into HOL Light
derivations.

The code also supports zChaff by using a translator from zChaff to
MiniSat proof format. See the subdirectory "zc2mso" and the README
file there for more information about the use of zChaff.

Most of this code was written by Hasan Amjad (see CREDITS for more
detail).

To use this code, you need to have a copy of MiniSat, specifically its
proof-logging version "MiniSat-p" installed. For downloads, see:

  http://minisat.se/MiniSat.html

The recommended version is this one, specifically:

  http://minisat.se/downloads/MiniSat-p_v1.14.2006-Sep-07.src.zip

I found that there can be a few problems compiling MiniSat with
modern C++ compilers (specifically g++ version 13), possibly
solved by:

 * Replacing "uint" with "uint32_t"

 * Replacing instances of "throw(whatever)" by "noexcept(false)"

By default, the code will look for MiniSat on your PATH. If it
doesn't find it, you can explicitly indicate the directory that
contains the MiniSat binary by changing the assignment of the
variable "satdir" defined on line 63, e.g.

  let satdir = "/home/johnh/bin/"

(The expected name for the binary within this directory is "minisat"
or "minsat.exe" according to platform. You can change this if desired
by modifying "SatSolvers.ml".)

Then you can load the code from this directory

  #use "Minisat/make.ml";;

and a new tautology-proving function SAT_PROVE is made available.
This can be used either to prove tautologies:

  # SAT_PROVE `p ==> p`;;
  val it : thm = |- p ==> p

or to provide, via an exception, a counterexample for non-tautologies:

  # SAT_PROVE `p==> q`;;
  Exception: Sat_counterexample |- ~q /\ p ==> ~(p ==> q).

There is a file here called "taut.ml" containing some larger examples.

Note that the code uses OCaml's string [Str] library. This is normally
loaded dynamically, but on some platforms such as Cygwin you may need to
construct a new OCaml toplevel explicitly including it before loading
HOL Light, using for example:

 ocamlmktop -o ocamlnumunixstr unix.cma nums.cma str.cma

since HOL Light already needs the "Unix" and "num" libraries anyway.
