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-<!-- FIXME: would be nice to provide links from features
-  mentioned here to user-manual. -->
-<h2>Features of Proof General</h2>
-<p>
-It doesn't matter if you're an Emacs militant or a pacifist!
-</p>
-
-<p> The aim of Proof General is to provide powerful and configurable
-interfaces which help user-interaction with proof assistants.  Proof
-General targets power users rather than novices, but is designed to be
-useful to both.  Proof General leads to an environment for serious
-<i>proof engineering</i> of interactively-constructed proofs.
-</p>
-<p>Proof General is used by many people for organizing large proof
-developments, and also for teaching interactive proof. 
-They enjoy the following features:</p>
-</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.  Bodies of completed proofs in the locked region
-  can be hidden from view to help browsing.  
-  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">screenshots</a>
-  of Proof General to see script management in action.
-  </p>
-  </dd>
-</dl><dl>
-  <?php dt("Simplified interaction model","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>
-</dl><dl>
-  <?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>
-</dl><dl>
-  <?php dt("Subterm highlighting and proof by pointing","pbp") ?>
-  <dd>
-  <p>
-  Using hidden markup in the concrete syntax, Proof General allows the
-  user to explore the structure of complex terms output by the prover.
-  This provides nifty features for cutting-and-pasting subterms,
-  querying the type of a subterm, looking up the definition of an
-  identifier, and so on.
-  </p>
-  <p>
-  <em>Proof by pointing</em> uses this markup to allow the prover
-  to suggest steps in a proof, guided by the user's gestures
-  in displayed goals.  For example, clicking on a hypothesis inserts 
-  a proof step into the script to solve a goal using that hypothesis, 
-  and executes it.
-  </p>
-  <?php footnote("Subterm markup is only fully supported by LEGO at the moment, with an experimental implementation of proof by pointing.  Isabelle highlights only variables.  If you would like to see these features better supported in your favourite proof assistant, please canvas the implementor to add subterm-markup support.")  ?>
-  </dd>
-</dl><dl>
-  <?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>
-  </dd>
-</dl><dl>
-  <?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>
-</dl><dl>
-  <?php dt("Real symbols","xsymbol") ?>
-  <dd>
-  Proof General has a close integration with the
-  powerful 
-  <a href="http://x-symbol.sourceforge.net/">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 "&not; P", instead
-   of "a * b", you see "a &times; b", etc. 
-  <br>
-   (Those examples are simple so they will work on most browsers 
-    without needing images, see the
-    <a href="screenshot">screenshots</a> for more examples.)
-  <p>
-  </dd>
-</dl><dl>
-  <?php dt("Proof-script editing facilities","funcmenu") ?>
-  <dd>
-  <p>
-  Many facilities are provided for editing proof scripts.   
-  The <i>completion</i> mechanism of Emacs can be used to
-  help type keywords and identifier names.
-  The <i>outline</i> mode of Emacs allows hiding of parts of proof scripts;
-  a further special <i>proof hiding</i> facility is provided to
-  hide the body of completed proofs.
-  <i>Navigation</i> in the script is supported by a pull-down menu 
-  which gives easy access to the theorems, definitions, and declarations
-  in the current buffer.  
-  </p>
-<!-- it is in FSF Emacs if you download func-menu.el from somewhere -->
-<!--   <?php footnote("Definitions menu is available in XEmacs only") ?> -->
-  <p>
-  </dd>
-</dl><dl>
-  <?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>
-</dl><dl>
-  <?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>
-</dl><dl>
-  <?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.html","tell us ","Feedback form")?>
-  how you get on.
-  </dd>
-</dl>
-<p>
-For (even) more details of Proof General's features, see the manuals and
-papers on the <a href="doc">documentation page</a>.
-</p>
-