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<h2>Features of Proof General</h2>
<p>
It doesn't matter if you're an Emacs militant or a pacifist!
</p>
<p>
Proof General is designed to be useful for novices and expert users alike.
<br>
It will be useful to you if you use a proof assistant, and
you'd like an interface with the following features...
</p>
<dl>
<?php dt("Script management","script") ?>
<dd>
A <em>proof script</em> is a sequence of commands sent to
a proof assistant to construct a proof, usually stored in
a file. <em>Script management</em> connects the editing of a
proof script directly to an interactive proof process,
maintaining consistency between the edit buffer
and the state of the proof assistant.
<p>
Proof General colours a proof script to show the state in the proof
assistant. Parts of a proof script that have been processed are
displayed in blue and are "locked" -- they cannot be edited. Parts
of the script currently being processed by the proof assistant are
shown in red. Proof General has commands for processing new parts
of the buffer, or undoing already processed parts.
</p>
<p>
Take a look at these
<a href="screenshot.phtml">screenshots</a>
of Proof General to see script managament in action.
</p>
</dd>
<?php dt("Simplified interaction","simple") ?>
<dd>
Proof General is designed for proof assistants which have a
command-line shell interpreter. When using Proof General, the proof
assistant's shell is hidden from the user. Communication takes
place via three buffers (Emacs text widgets). The <i>script
buffer</i> holds input, the commands to construct a proof. The
<i>goals buffer</i> displays the current list of subgoals to be
solved. The <i>response buffer</i> displays other output from the
proof assistant. By default, only two of these three buffers are
displayed at once. This means that the user only sees the output
from the most recent interaction, rather than a screen full of
output from the proof assistant.
<p>
Despite this more friendly communication model, Proof General does not
commandeer the proof assistant shell: the user still has complete
access to it if necessary.
</p>
</dd>
<?php dt("Multiple files","multiple") ?>
<dd>
Script management in Proof General can work across many script
files, integrating with the file handling of
the proof assistant. When a script is visited in the editor, it
is locked (coloured) to reflect whether the proof assistant has
loaded it in this session. When a file is unlocked, all of the
files which depend on it are automatically unlocked too.
<p>
Dependencies between script files are either communicated from the
proof assistant to Proof General, or maintained automatically by
Proof General (based on the order in which files were processed).
</p>
</dd>
<?php dt("Proof by Pointing","pbp") ?>
<dd>
<em>Proof by pointing</em> allows you to click on a subterm of
a goal to be proved, and apply an appropriate rule or
tactic automatically.
<p>
Proof by pointing uses the interface to highlight subterms under the
mouse, and sends messages asking the prover for hints to proceed.
Proof General also uses the subterm structure to make it easy to cut
and paste from complicated terms.
</p>
<?php footnote("Proof by pointing for Proof General is only supported by LEGO (experimentally) at the moment. For others, we need help from each proof assistant implementor to add support for their system. Please canvas the implementor of your favourite
proof assistant to add PBP support.") ?>
</dd>
<?php dt("Toolbar and menus","toolbar") ?>
<dd>
Proof General has a toolbar with buttons for examining
the proof state, starting a proof, manoeuvring in the proof script,
restarting the prover, saving a proof, searching for a theorem,
issuing a command, interrupting the assistant, and getting help.
<p>
Using the toolbar, you can replay proofs without knowing any
low-level commands of the proof assistant or any Emacs hot-keys!
<p>
Additionally, the toolbar commands and many more besides are
available on menus; you don't need to know magical key presses for
any features.
</p>
<?php footnote("Toolbar is available in XEmacs only") ?>
</dd>
<?php dt("Syntax highlighting","fontlock") ?>
<dd>
Syntax highlighting is an editing feature which decorates a file
with different colours or fonts according to the syntax of some
language (usually a programming language).
<p>
Proof General decorates proof scripts: proof commands are
highlighted and different fonts may be used for definitions and
assumptions, for example.
</p>
</dd>
<?php dt("Real symbols","xsymbol") ?>
<dd>
Proof General has a close integration with the
powerful
<a href="http://www.fmi.uni-passau.de/~wedler/x-symbol">X-Symbol</a>
package, which makes it easy to transparently use real symbols and
Greek letters in your proofs.
<br>
Instead of seeing "not P", you see "¬ P", instead
of "a * b", you see "a × b", etc.
<br>
(Those examples are simple so they will work on most browsers
without needing images, see the
<a href="screenshot.phtml">screenshots</a> for more examples.)
<p>
<?php footnote("X-Symbol currently works in XEmacs only") ?>
</dd>
<?php dt("Functions Menu","funcmenu") ?>
<dd>
A pull-down menu gives easy
navigations to theorems, definitions, and declarations
proved in the current buffer.
<!-- it is in FSF Emacs if you download func-menu.el from somewhere -->
<!-- <?php footnote("Definitions menu is available in XEmacs only") ?> -->
<p>
</dd>
<?php dt("Remote proof assistant.") ?>
<dd>
Sometimes you may want to run a proof assistant on a powerful remote
machine. Proof General can communicate with a proof assistant running
remotely, while your files and editor reside on your local machine.
<p></p>
</dd>
<?php dt("Tags","tags") ?>
<dd>
Tags are an editing feature which allow you to quickly locate the
definition or declaration of a particular identifier. Proof General
is supplied with utilities to make tag indexes for Emacs.
This makes it easy to quickly access
definitions from a standard library, for example, and in large proof
developments split across multiple files.
<!-- <?php footnote("Tags programs are provided for LEGO and Coq") ?> -->
<p></p>
</dd>
<?php dt("Adaptability","generic") ?>
<dd>
Proof General is designed to be adaptable. Many aspects
of its behaviour can be easily customized (using dialogue boxes and
buttons, no text file editing!).
<p>
Most importantly, Proof General is generic, so you can adapt it to
a new proof assistant with surprisingly little effort.
<p>
Adapting for a new proof assistant is mainly a matter of setting
some variables with regular expressions to help parse output from
the prover, and setting other variables with commands to send to the
prover. See this basic
<?php fileshow("ProofGeneral/demoisa/demoisa-easy.el",
"example instance"); ?>.
To get the most from Proof General (proof by pointing, for
example), it may be necessary to put some hooks in
the output routines of the proof assistant.
</p>
Please feel free to download Proof General to customize it for a new
system, and
<?php hlink("feedback.phtml","tell us ","Feedback form")?>
how you get on.
</dd>
</dl>
<p>
For (even) more details of the above features, see the
<?php link_root("doc","documentation page.") ?>
</p>
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