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Translating an LTL formula into a never claim

Table of Contents

Here is how to translate an LTL (or PSL) formula into a never claim.

Shell

ltl2tgba --spin 'GFa -> GFb'
never { /* F(GFb | G!a) */
T0_init:
  if
  :: (!(a)) -> goto accept_S0
  :: (true) -> goto T0_init
  :: (b) -> goto accept_S2
  fi;
accept_S0:
  if
  :: (!(a)) -> goto accept_S0
  fi;
accept_S2:
  if
  :: (b) -> goto accept_S2
  :: (!(b)) -> goto T0_S3
  fi;
T0_S3:
  if
  :: (b) -> goto accept_S2
  :: (!(b)) -> goto T0_S3
  fi;
}

Python

The formula function returns a formula object (or raises a parse-error exception). Formula objects have a translate() method that returns an automaton, and the automata objects have a to_str method that can output in one of the supported syntaxes.

So the translation is actually a one-liner in Python:

import spot
print(spot.formula('GFa -> GFb').translate('BA').to_str('spin'))

The above line can actually be made a bit shorter, because translate() can also be used as a function (as opposed to a method) that takes a formula (possibly as a string) as first argument:

import spot
print(spot.translate('GFa -> GFb', 'BA').to_str('spin'))

C++

All the translation pipeline (this include simplifying the formula, translating the simplified formula into an automaton, and simplifying the resulting automaton) is handled by the spot::translator class. An instance of this class can configured by calling set_type() to chose the type of automaton to output, set_level() to set the level of optimization (it's high by default), and set_pref() to set various preferences (like small or deterministic) or characteristic (complete, unambiguous) for the resulting automaton. Finally, the output as a never claim is done via the print_never_claim function.

#include <iostream>
#include <spot/tl/parse.hh>
#include <spot/twaalgos/translate.hh>
#include <spot/twaalgos/neverclaim.hh>

int main()
{
  spot::parsed_formula pf = spot::parse_infix_psl("[]<>p0 || <>[]p1");
  if (pf.format_errors(std::cerr))
    return 1;
  spot::translator trans;
  trans.set_type(spot::postprocessor::BA);
  spot::twa_graph_ptr aut = trans.run(pf.f);
  print_never_claim(std::cout, aut) << '\n';
  return 0;
}
never {
T0_init:
  if
  :: (p1) -> goto accept_S0
  :: (true) -> goto T0_init
  :: (p0) -> goto accept_S2
  fi;
accept_S0:
  if
  :: (p1) -> goto accept_S0
  fi;
accept_S2:
  if
  :: (p0) -> goto accept_S2
  :: (!(p0)) -> goto T0_S3
  fi;
T0_S3:
  if
  :: (p0) -> goto accept_S2
  :: (!(p0)) -> goto T0_S3
  fi;
}

Additional comments

The Python version of translate() is documented as follows:

import spot
help(spot.translate)