add ltlsynt executable

For now, ltlsynt only handles LTL realizability. It uses a reduction to
parity game followed by Calude et al.'s reduction from parity game to
reachability game.

* bin/ltlsynt.cc, bin/Makefile.am, bin/man/ltlsynt.x,
bin/man/Makefile.am, bin/.gitignore: New binary.
* doc/org/arch.tex, doc/Makefile.am, doc/org/tools.org,
doc/org/ltlsynt.org: Document it.
* spot/misc/game.cc, spot/misc/game.hh, spot/misc/Makefile.am: Parity
game wrapper for parity automata + reachability game interface from
Calude et al.'s paper.

doc/Makefile.am

@@ -100,6 +100,7 @@ ORG_FILES = \
   org/ltldo.org \
   org/ltlfilt.org \
   org/ltlgrind.org \
+  org/ltlsynt.org \
   org/oaut.org \
   org/randaut.org \
   org/randltl.org \

doc/org/arch.tex

@@ -28,6 +28,7 @@
     \texttt{dstar2tgba}\\
     \texttt{ltlcross}\\
     \texttt{ltlgrind}\\
+    \texttt{ltlsynt}\\
     \texttt{ltldo}\\
     \texttt{autcross}
   };

doc/org/ltlsynt.org

@@ -0,0 +1,55 @@
+# -*- coding: utf-8 -*-
+#+TITLE: =ltlsynt=
+#+DESCRIPTION: Spot command-line tool for synthesizing AIGER circuits from LTL/PSL formulas.
+#+SETUPFILE: setup.org
+#+HTML_LINK_UP: tools.html
+
+* Basic usage
+
+This tool answers whether a controller can be built given an LTL/PSL formula
+specifying its behavior.  =ltlsynt= is typically called with
+the following three options:
+
+- =--input=: a comma-separated list of input signal names
+- =--output=: a comma-separated list of output signal names
+- =--formula= or =--file=: the LTL/PSL specification.
+
+The following example is unrealizable, because =a= is an input, so no circuit
+can guarantee that it will be true eventually.
+
+#+BEGIN_SRC sh :results verbatim :exports both
+ltlsynt --input=a --output=b -f 'F a'
+#+END_SRC
+
+#+RESULTS:
+#+begin_example
+UNREALIZABLE
+#+end_example
+
+* TLSF
+
+=ltlsynt= was made with the [[http://syntcomp.org/][SYNTCOMP]] competition in
+mind, and more specifically the TLSF track of this competition.  TLSF is a
+high-level specification language created for the purpose of this competition.
+Fortunately, the SYNTCOMP organizers also provide a tool called =syfco= which
+can translate a TLSF specification to an LTL formula.
+
+The following four steps show you how a TLSF specification called spec.tlsf can
+be tested for realizability using =syfco= and =ltlsynt=:
+
+#+BEGIN_SRC sh
+LTL=$(syfco FILE -f ltlxba -m fully)
+IN=$(syfco FILE -f ltlxba -m fully)
+OUT=$(syfco FILE -f ltlxba -m fully)
+ltlsynt --formula="$LTL" --input="$IN" --output="$OUT"
+#+END_SRC
+
+* Algorithm
+
+The tool reduces the synthesis problem to a parity game, and solves the parity
+game using Zielonka's recursive algorithm.  The full reduction from LTL to
+parity game is described in a paper yet to be written and published.
+
+You can ask =ltlsynt= not to solve the game and print it instead (in the
+PGSolver format) using the =--print-pg= option, and leaving you the choice of
+an external solver such as PGSolver.

doc/org/tools.org

@@ -49,6 +49,7 @@ corresponding commands are hidden.
   formula.
 - [[file:ltldo.org][=ltldo=]] Run LTL/PSL formulas through other tools using common [[file:ioltl.org][input]]
   and [[file:oaut.org][output]] interfaces.
+- [[file:ltlsynt.org][=ltlsynt=]] Synthesize AIGER circuits from LTL/PSL specifications.
 - [[file:dstar2tgba.org][=dstar2tgba=]] Convert \omega-automata with any acceptance into
   variants of Büchi automata.
 - [[file:randaut.org][=randaut=]] Generate random \omega-automata.
@@ -73,8 +74,9 @@ convenience, you can browse their HTML versions:
 [[./man/ltl2tgta.1.html][=ltl2tgta=]](1),
 [[./man/ltlcross.1.html][=ltlcross=]](1),
 [[./man/ltldo.1.html][=ltldo=]](1),
-[[./man/ltlgrind.1.html][=ltlgrind=]](1),
 [[./man/ltlfilt.1.html][=ltlfilt=]](1),
+[[./man/ltlgrind.1.html][=ltlgrind=]](1),
+[[./man/ltlsynt.1.html][=ltlsynt=]](1),
 [[./man/randaut.1.html][=randaut=]](1),
 [[./man/randltl.1.html][=randltl=]](1),
 [[./man/spot-x.7.html][=spot-x=]](7),