HOL Proof General, for HOL 98.

Written by David Aspinall.

$Id$

This is a "technology demonstration" of Proof General for HOL 98.

It may well work with other versions of HOL, but is untested (please
let me know if you try).

It has basic script management support, with a little bit of
decoration of scripts and output.

There is support for x-symbols, but not using a proper token language.
Try writing "philosophy" !

I have written this in the hope that somebody from the HOL community
will adopt it and turn it into a proper instantiation of 
Proof General.

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Note:

There are some problems at the moment.  HOL proof scripts often use
batch-oriented single step tactic proofs, but Proof General does not
offer an easy way to edit these kind of proofs.  The "Boomburg" Emacs
interface by Koichi Takahashi and Masima Hagiya addressed this, and to
some extent so does the Emacs interface supplied with HOL.  Perhaps
one of these could be embedded inside Proof General.  Implemented in
a generic way, managing batch vs interactive proofs would also be
useful for Isabelle.

Another problem is that HOL scripts sometimes use SML structures,
which can cause confusion because Proof General does not really parse
SML, it just looks for semicolons.  Again, this could be improved by
taking a better parser (e.g. from sml mode).

These improvements would be worthwhile contributions to Proof General
and also provide the HOL community with a nice front end.  
Please have a go!