# -*- 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 synthesizes [[http://fmv.jku.at/aiger/][AIGER]] circuits from LTL/PSL
formulas.  =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 illustrates the synthesis of an =AND= gate.  We call the two
inputs =a= and =b=, and the output =c=.  We want the relationship between the
inputs and the output to always hold, so we prefix the propositional formula
with a =G= operator:

#+BEGIN_SRC sh :results verbatim :exports both
ltlsynt --input=a,b --output=c --formula 'G (a & b <=> c)'
#+END_SRC

#+RESULTS:
#+begin_example
REALIZABLE
aag 3 2 0 1 1
2
4
6
6 2 4
i0 a
i1 b
o0 c
#+end_example

The output is composed of two sections.  The first one is a single line
containing either REALIZABLE or UNREALIZABLE, and the second one is an AIGER
circuit that satisfies the specification (or nothing if it is unrealizable).
In this example, the generated circuit contains, as expected, a single =AND=
gate linking the two inputs to the output.

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 synthesized 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 control the parity game solving step in two ways:
- By choosing a different algorithm using the =--algo= option. The default is
=rec= for Zielonka's recursive algorithm, and as of now the only other
available option is =qp= for Calude et al.'s quasi-polynomial time algorithm.
- By asking =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.