* src/ltlvisit/simplify.hh (ltl_simplifier_options): add
a boolean_to_isop option
(ltl_simplifier::boolean_to_isop): New method.
* src/ltlvisit/simplify.cc: Implement these.
* src/bin/ltlfilt.cc: Add a --boolean-to-isop option.
* src/ltltest/isop.test: New file.
* src/ltltest/Makefile.am: Add it.
* NEWS: Mention it.

GF(a|Xb) = GF(a|b)      GF(a|Fb) = GF(a|b)
FG(a&Xb) = FG(a&b)      FG(a&Gb) = FG(a&b)

* src/ltlvisit/simplify.cc: Implement them.
* NEWS, doc/tl/tl.tex: Document them.
* src/ltltest/reduccmp.test: Test then.

* src/bin/common_finput.cc, src/tgbaalgos/lbtt.cc: Use !empty() instead
of size() > 0.
* src/bin/ltl2tgta.cc, src/kripke/kripkeexplicit.cc,
src/tgbatest/complementation.cc: Avoid useless assignments.
* src/bin/ltlcross.cc: Correct mistaken assignment inside assert().
* src/evtgba/symbol.hh, src/tgba/tgbabddcoredata.cc,
src/tgba/tgbabddcoredata.hh,
src/tgba/tgbasafracomplement.cc (operator=): Do not return a const
reference.
* src/evtgbatest/ltl2evtgba.cc, src/evtgbatest/product.cc,
src/evtgbatest/product.cc: Check indices before using them, not after.
* src/kripke/kripkeexplicit.cc, src/kripke/kripkeexplicit.hh,
src/tgbatest/randtgba.cc: Pass constant strings by reference.
* src/kripke/kripkeprint.cc, src/tgbaalgos/simulation.cc:
Remove a useless operation.
* src/ltlvisit/simplify.cc: Remove a duplicate condition.
* src/misc/formater.hh: Remove unused attribute.
* src/misc/modgray.cc: Initialize done_ in the constructor.
* src/saba/explicitstateconjunction.cc,
src/saba/explicitstateconjunction.hh (operator=): Fix prototype.
* src/saba/sabacomplementtgba.cc: Remove unused default constructor.
* src/ta/taexplicit.cc, src/ta/taproduct.cc, src/ta/tgtaproduct.cc,
src/ta/tgtaproduct.hh, src/taalgos/emptinessta.cc,
src/taalgos/minimize.cc, src/taalgos/reachiter.cc,
src/taalgos/tgba2ta.cc, src/tgbaalgos/cutscc.cc: Use C++ casts, and
++it instead of it++.
* src/taalgos/dotty.cc, src/tgbatest/ltl2tgba.cc: Refine the scope of
variables.
* src/tgba/tgbakvcomplement.hh (bdd_order): Always initialize bdd_.
* src/tgba/tgbasgba.cc, src/tgba/wdbacomp.cc: Use the initialization
line to initialize all members.

* NEWS: Mention this.
* COPYING: Replace by GPL v3.
* src/sanity/style.test: Check files with the wrong license,
in case we forgot to update it during a merge.
* Makefile.am, bench/Makefile.am, bench/emptchk/Makefile.am,
bench/emptchk/defs.in, bench/emptchk/ltl-human.sh,
bench/emptchk/ltl-random.sh, bench/emptchk/pml-clserv.sh,
bench/emptchk/pml-eeaean.sh, bench/emptchk/pml2tgba.pl,
bench/ltl2tgba/big, bench/ltl2tgba/defs.in, bench/ltl2tgba/known,
bench/ltl2tgba/lbtt2csv.pl, bench/ltl2tgba/ltl2baw.in,
bench/ltl2tgba/parseout.pl, bench/ltl2tgba/small,
bench/ltlclasses/Makefile.am, bench/ltlclasses/defs.in,
bench/ltlclasses/run, bench/ltlcounter/Makefile.am,
bench/ltlcounter/defs.in, bench/ltlcounter/run,
bench/scc-stats/Makefile.am, bench/scc-stats/stats.cc,
bench/split-product/Makefile.am, bench/split-product/cutscc.cc,
bench/split-product/pml2tgba.pl, bench/wdba/Makefile.am,
bench/wdba/defs.in, bench/wdba/run, configure.ac, doc/Makefile.am,
doc/dot.in, doc/tl/Makefile.am, ifac...

* src/ltlvisit/simplify.cc: Here.
* doc/tl/tl.tex: Document them.
* src/ltltest/reduccmp.test: Test them.

* src/ltlvisit/simplify.cc: Add them.
* src/ltltest/reduccmp.test: Check them.
* doc/tl/tl.tex: Document them.

* src/ltlvisit/simplify.hh, src/ltlvisit/simplify.cc: Here.

* src/ltlvisit/simplify.cc, src/ltlvisit/simplify.hh: Add a
implication() option.
* src/bin/ltlfilt.cc: Add options --implied-by, --imply, and
--equivalent-to.

* src/ltlvisit/simplify.cc, src/tgba/tgbaproduct.cc,
src/tgba/tgbatba.cc, src/tgbaalgos/sccfilter.cc,
src/tgbaalgos/simulation.cc: Here.

* src/eltlparse/Makefile.am, src/ltlvisit/randomltl.cc,
src/ltlvisit/simplify.cc, src/ltlvisit/snf.cc, src/ltlvisit/snf.hh:
Fix GPL to version 2 or later.

Doing so will release all BDD variables used by automata created for
syntactic implication.  This way the main translation will create
acceptance variables again in a more natural order, which will help
the degeneralization (until we get a better degeneralization).

* src/ltlvisit/contain.cc, src/ltlvisit/contain.hh
(language_containment_checker::clear): New method to clear the
containment cache.
* src/ltlvisit/simplify.cc, src/ltlvisit/simplify.hh
(clear_as_bdd_cache): Also call language_containment_checker::clear.

Syntactic implication checks may use as_bdd() to compare Boolean
formulae.  By doing so, they register Boolean variables in an order
that is usially detrimental to the LTL translator.  The new,
clear_as_bdd_cache() function offers a mean to unregister these
variables, so that the LTL translator will register them again in the
a more natural way.

* src/ltlvisit/simplify.hh, src/ltlvisit/simplify.cc
(clear_as_bdd_cache): New function.
* src/tgbatest/ltl2tgba.cc, wrap/python/ajax/spot.in: Call it.

* src/ltlvisit/simplify.cc
(ltl_simplifier_cache::syntactic_implication): If the lhs and rhs are
literals that are not equal, return false immediately.

* src/ltlvisit/simplify.cc, src/ltlvisit/simplify.hh (print_stats):
New function.
* src/tgbatest/ltl2tgba.cc: Call it.

We need a marked version of !{r} to perform breakpoint unroling.

* src/ltlast/unop.cc, src/ltlast/unop.hh: Declare a NegClosureMarked
operator.
* src/ltlvisit/mark.hh, src/ltlvisit/mark.cc,
src/tgbaalgos/ltl2tgba_fm.cc: Adjust to deal with NegClosureMarked
and NegClosure as apropriate.
* src/ltlvisit/simplify.cc, src/ltlvisit/tostring.cc,
src/ltlvisit/tunabbrev.cc, src/tgbaalgos/eltl2tgba_lacim.cc,
src/tgbaalgos/ltl2taa.cc, src/tgbaalgos/ltl2tgba_lacim.cc,
src/tgba/formula2bdd.cc: Deal with NegClosureMarked in the same way as
we deal with NegClosure.
* src/tgbatest/ltl2tgba.test: More tests.
* src/ltltest/kind.test: Adjust.
* doc/tl/tl.tex: Mention the marked negated closure.

* doc/tl/tl.tex, src/ltlvisit/simplify.cc: Fix the rule.
* src/ltltest/reduccmp.test, src/ltltest/syntimpl.test:
Add more tests.

* src/ltlvisit/simplify.cc (reduce_sere_ltl): Here.
* src/ltltest/reduccmp.test: Add a test case.

The distinction makes no sense since Spot 0.5, where we switched from
mutable furmulae to immutable formulae.  The difference between
const_visitor and visitor made no sense either.  They have been merged
into one: visitor.

* iface/dve2/dve2check.cc, iface/gspn/ltlgspn.cc,
src/eltlparse/eltlparse.yy, src/eltlparse/public.hh,
src/evtgbatest/ltl2evtgba.cc, src/kripkeparse/kripkeparse.yy,
src/ltlast/atomic_prop.cc, src/ltlast/atomic_prop.hh,
src/ltlast/automatop.cc, src/ltlast/automatop.hh, src/ltlast/binop.cc,
src/ltlast/binop.hh, src/ltlast/bunop.cc, src/ltlast/bunop.hh,
src/ltlast/constant.cc, src/ltlast/constant.hh, src/ltlast/formula.cc,
src/ltlast/formula.hh, src/ltlast/formula_tree.cc,
src/ltlast/formula_tree.hh, src/ltlast/multop.cc,
src/ltlast/multop.hh, src/ltlast/predecl.hh, src/ltlast/refformula.cc,
src/ltlast/refformula.hh, src/ltlast/unop.cc, src/ltlast/unop.hh,
src/ltlast/visitor.hh, src/ltlenv/declenv.cc, src/ltlenv/declenv.hh,
src/ltlenv/defaultenv.cc, src/ltlenv/defaultenv.hh,
src/ltlenv/environment.hh, src/ltlparse/ltlfile.cc,
src/ltlparse/ltlfile.hh, src/ltlparse/ltlparse.yy,
src/ltlparse/public.hh, src/ltltest/consterm.cc,
src/ltltest/equals.cc, src/ltltest/genltl.cc, src/ltltest/kind.cc,
src/ltltest/length.cc, src/ltltest/randltl.cc, src/ltltest/readltl.cc,
src/ltltest/reduc.cc, src/ltltest/syntimpl.cc,
src/ltltest/tostring.cc, src/ltlvisit/apcollect.cc,
src/ltlvisit/apcollect.hh, src/ltlvisit/clone.cc,
src/ltlvisit/clone.hh, src/ltlvisit/contain.cc,
src/ltlvisit/contain.hh, src/ltlvisit/dotty.cc,
src/ltlvisit/length.cc, src/ltlvisit/lunabbrev.cc,
src/ltlvisit/lunabbrev.hh, src/ltlvisit/mark.cc, src/ltlvisit/mark.hh,
src/ltlvisit/nenoform.cc, src/ltlvisit/nenoform.hh,
src/ltlvisit/postfix.cc, src/ltlvisit/postfix.hh,
src/ltlvisit/randomltl.cc, src/ltlvisit/randomltl.hh,
src/ltlvisit/reduce.cc, src/ltlvisit/reduce.hh,
src/ltlvisit/simpfg.cc, src/ltlvisit/simpfg.hh,
src/ltlvisit/simplify.cc, src/ltlvisit/simplify.hh,
src/ltlvisit/snf.cc, src/ltlvisit/snf.hh, src/ltlvisit/tostring.cc,
src/ltlvisit/tunabbrev.cc, src/ltlvisit/tunabbrev.hh,
src/ltlvisit/wmunabbrev.cc, src/ltlvisit/wmunabbrev.hh,
src/neverparse/neverclaimparse.yy, src/sabatest/sabacomplementtgba.cc,
src/tgba/bdddict.cc, src/tgba/formula2bdd.cc, src/tgba/taatgba.cc,
src/tgba/taatgba.hh, src/tgbaalgos/eltl2tgba_lacim.cc,
src/tgbaalgos/ltl2taa.cc, src/tgbaalgos/ltl2tgba_fm.cc,
src/tgbaalgos/ltl2tgba_lacim.cc, src/tgbaalgos/minimize.cc,
src/tgbaalgos/randomgraph.cc, src/tgbaparse/tgbaparse.yy,
src/tgbatest/complementation.cc, src/tgbatest/ltl2tgba.cc,
src/tgbatest/ltlprod.cc, src/tgbatest/mixprod.cc,
src/tgbatest/randtgba.cc: Massive adjustment!
* src/tgbatest/reductgba.cc: Delete.

* src/ltlvisit/simplify.cc: Here.
* src/ltltest/reduccmp.test: Test them.
* doc/tl/tl.tex: Document them.

* src/ltlvisit/simplify.cc: Here.
* src/ltltest/reduccmp.test: Test it.
* doc/tl/tl.tex: Document it.

* src/ltlvisit/simplify.cc: Here.
* src/ltltest/reduccmp.test: Test them.
* doc/tl/tl.tex: Document them.

* src/ltlvisit/simplify.cc (reduce_sere_ltl): New function,
to factor the code of the []-> and <>-> rewrittings.
* src/ltltest/reduccmp.test: Add more tests.
* doc/tl/tl.tex: Document these rewritings.

* src/ltlvisit/simplify.cc: Here.
* doc/tl/tl.tex: Document then.
* src/ltlast/bunop.hh (as_KleenStar): New helper function.
* src/ltltest/reduccmp.test: Add more tests.
* src/ltltest/reduc.cc: Also display the resulting formula
without reduce_size_stricly.

* src/ltlvisit/snf.cc, src/ltlvisit/snf.hh: New files.
* src/ltlvisit/Makefile.am: Distribute them.
* src/ltlvisit/simplify.cc, src/ltlvisit/simplify.hh: Call snf(f) for
all f[*].
* src/ltltest/reduccmp.test: Test it.
* doc/tl/tl.tex, doc/tl/tl.bib: Document it.

It was a mistake to try to overload And/Or LTL operator for these when
trivial simplification are performed.  The reason is so simple it is
embarassing: And(f,1)=f is a trivial identity that should not be
applied with AndRat.  E.g. AndRat(a;b, 1) is equal to 0, not a;b.

* src/ltlast/multop.hh, src/ltlast/multop.cc: Add the AndRat and OrRat
operators.
* src/ltlparse/ltlparse.yy: Build them.
* src/ltlvisit/mark.cc, src/ltlvisit/simplify.cc,
src/ltlvisit/tostring.cc, src/tgba/formula2bdd.cc,
src/tgbaalgos/eltl2tgba_lacim.cc, src/tgbaalgos/ltl2taa.cc,
src/tgbaalgos/ltl2tgba_fm.cc, src/tgbaalgos/ltl2tgba_lacim.cc:
Adjust all switches.

* src/ltlvisit/simplify.cc: Here.
* src/ltltest/reduccmp.test: More tests.
* doc/tl/tl.tex: Document them.

* src/ltlast/bunop.hh, src/ltlast/bunop.cc, src/ltlvisit/randomltl.cc,
src/ltlvisit/simplify.cc, src/ltlvisit/tostring.cc,
src/tgbaalgos/ltl2tgba_fm.cc: Remove all traces of these two
operators since they are not handled like sugar.
* doc/tl/tl.tex: Adjust documentation to reflect the fact that these
two operators are sugar.

* src/ltlvisit/simplify.cc (spot::ltl::is_And, spot::ltl::is_F,
spot::ltl::is_FG, spot::ltl::is_G, spot::ltl::is_GF, spot::ltl::is_M,
spot::ltl::is_Or, spot::ltl::is_R, spot::ltl::is_U, spot::ltl::is_W,
spot::ltl::is_X, spot::ltl::is_binop, spot::ltl::is_constant,
spot::ltl::is_multop, spot::ltl::is_unop): Move ...
* src/ltlast/binop.hh, src/ltlast/constant.hh, src/ltlast/multop.hh
src/ltlast/unop.hh: ... here, as appropriate.

* src/ltlvisit/simplify.cc: Use but_all() to simplify code.

* src/ltlast/multop.hh, src/ltlast/multop.cc (all_but): New method
used to simplify the removal of one element of a multop.
* src/ltlvisit/simplify.cc: Implement the new rewriting rules.
* doc/tl/tl.tex: Document them.
* src/ltltest/reduccmp.test: Test them.

* src/ltlvisit/simplify.hh (ltl_simplifier_options): New option
reduce_size_stricly.
* src/ltlvisit/simplify.cc (simplify_visitor): Implement these
rules.
* src/ltltest/reduc.cc: Check with reduce_size_strictly unset or
set, but only use the latter result to check sizes.
* src/ltltest/reduccmp.test: Test them.
* doc/tl/tl.tex: Document them.

* src/ltlvisit/simplify.cc: Add new rules.
* doc/tl/tl.tex: Document them.
* src/ltltest/reduccmp.test: Add test cases.

The actual rules are a bit more complex:
a & X(G(a&b...)&c...) = Ga & X(G(b...)&c...)
a | X(Fa | c) = F(a) | c
with the second rule being applied only if all XF can
be removed.  See the documentation for an example.

* src/ltlvisit/simplify.cc: Implement these new rules.
* doc/tl/tl.tex: Document them.
* src/ltltest/reduccmp.test: Add test cases.

* src/ltlvisit/simplify.cc: Implement these rules.
* src/ltltest/reduccmp.test: Add tests.
* doc/tl/tl.tex: Document them.

* src/ltlvisit/simplify.cc: Implement them here, and augment them
to support M, and W operators.
* src/ltltest/reduccmp.test: Add some tests.
* doc/tl/tl.tex (Simplifications Based on Implications): Document
these rules.
* doc/tl/tl.bib (babiak.12.tacas): New entry.

* src/ltlvisit/simplify.cc (simplify_visitor): Implement these
rules.
* doc/tl/tl.tex: Document these rules.

* src/ltlvisit/simplify.cc (simplify_visitor::visit(multop)):
Initialize `ri' to kill a warning.

* src/ltlvisit/simplify.cc: Add four rules.
* doc/tl/tl.tex: Document these rules.
* src/ltltest/reduccmp.test: Add tests.