* spot/twaalgos/toparity.cc: Do not call prpagate_marks_here twice if
the automaton was not degeneralized.
* spot/twaalgos/toparity.hh: Typo in comment.

Fixes #403.

* spot/twaalgos/cleanacc.cc (simplify_complementary_marks_here):
Assume that two colors are complementary in a broad sense, i.e., on is
present if (but not only if) the other is missing before applying
those rewritings.  Technically, this is usually not necessary, because
the changes done in #418 will cause such "covering-the-full-automaton"
pair of colors to be disjoint so complementary in a strict sense.  It
might make a difference (this is not tested) in presence of reused
colors which #418 cannot remove.  In any case, it's simply less code
to implement the broad sense.
* tests/python/toparity.py: Add test case from #403, which is
reduced to two states with recent optimizations.

This fixes issue #418.

* spot/twa/acc.cc,
spot/twa/acc.hh (acc_cond::acc_code::useless_colors_patterns): New
method to detect patterns of colors allowing other colors to be added
or removed at will.
* spot/twaalgos/cleanacc.cc (simplify_acceptance_here): Use the above
patterns to remove some useless colors from transitions and hope that
this can help simplify the acceptance condition.
* spot/twaalgos/degen.cc (propagate_marks_vector): Use the pattern to
add more colors.
* tests/core/ltl2tgba2.test: Add the test case from issue #418.
* tests/core/ltl2dstar4.test, tests/core/satmin3.test,
tests/core/sccdot.test, tests/core/sim3.test,
tests/python/automata.ipynb, tests/python/decompose.ipynb,
tests/python/merge.py, tests/python/pdegen.py, tests/python/remfin.py,
tests/python/toparity.py, tests/python/tra2tba.py: Adjust all test
cases.
* NEWS: Mention this new feature.

* spot/twaalgos/cleanacc.cc (merge_identical_marks_here, merge_mark,
included_marks): Fuse these into ...
(simplify_included_marks_here): ... this new function.
* NEWS: Mention the fix of issue #406.

* lib/argp-help.c (hol_entry_help): Handle cases with option
description is larger than RMARGIN.

* doc/org/spot.css: Display input and output closer and separate them
with dash.

* spot/twaalgos/remfin.cc: Actually use propmarks.
* tests/core/det.test, tests/core/remfin.test,
tests/python/automata.ipynb, tests/python/remfin.py,
tests/python/tra2tba.py: Adjust test cases.

This fixes #406.

* spot/twaalgos/cleanacc.cc: Add the simplification.
* tests/core/remfin.test, tests/python/automata.ipynb,
tests/python/remfin.py: Update tests.
* tests/python/simplacc.py: Update and add tests.

* spot/twaalgos/remfin.cc (tra_to_tba): Implement the same
optimization has in the generic remove_fin transformation.
* tests/python/tra2tba.py: Adjust.

Do not clone transitions that are necessarily part of on accepting
cycle in the main copy of the automaton.

* spot/twaalgos/remfin.cc: Use propagate_marks_vector to ignore more
edges.
* tests/core/remfin.test, tests/python/remfin.py,
tests/python/automata.ipynb: Adjust.
* tests/sanity/style.test: Do not choke on C++17 if statements with
initializer.

* doc/org/hierarchy.tex: Draw the shadow manually, so that it is part
of the bounding box when we extract the SVG.

This fixes #412.

* spot/twaalgos/translate.cc: Add the quick syntactic simplification.
* spot/twaalgos/relabel.cc: Do not register old unused APs.
* tests/core/ltl2tgba2.test: Add test case.
* tests/core/bdd.test, tests/python/automata.ipynb: Adjust.
* NEWS: Mention this.

Under that option, !(a ^ b) was converted
to (!a <=> !b) instead of simply (a <=> b).

* spot/tl/simplify.cc (equiv_or_xor): Improve
rewriting.
* tests/core/ltl2tgba2.test, tests/python/simstate.py: Adjust test
cases.

* configure.ac, NEWS, doc/org/setup.org: Set version to 2.9.3.

* doc/org/autcross.org, doc/org/autfilt.org, doc/org/citing.org,
doc/org/compile.org, doc/org/concepts.org, doc/org/csv.org,
doc/org/dstar2tgba.org, doc/org/genaut.org, doc/org/genltl.org,
doc/org/hierarchy.org, doc/org/hoa.org, doc/org/index.org,
doc/org/install.org, doc/org/ltl2tgba.org, doc/org/ltl2tgta.org,
doc/org/ltlcross.org, doc/org/ltlfilt.org, doc/org/ltlgrind.org,
doc/org/ltlsynt.org, doc/org/oaut.org, doc/org/randaut.org,
doc/org/randltl.org, doc/org/satmin.org, doc/org/tut.org,
doc/org/tut01.org, doc/org/tut02.org, doc/org/tut03.org,
doc/org/tut04.org, doc/org/tut10.org, doc/org/tut11.org,
doc/org/tut12.org, doc/org/tut20.org, doc/org/tut21.org,
doc/org/tut22.org, doc/org/tut23.org, doc/org/tut24.org,
doc/org/tut30.org, doc/org/tut31.org, doc/org/tut50.org,
doc/org/tut51.org, doc/org/tut52.org, doc/org/tut90.org,
doc/org/upgrade2.org: Run ispell-buffer on all these.
* bin/autfilt.cc, python/spot/__init__.py: Fix typos in
help texts noticed while spell-checking the org files.

* doc/org/.dir-locals.el.in, doc/org/init.el.in: Set the
SPOT_UNINSTALLED envvar, as we already do in the test suite.

Reported by Salomon Sickert.

* bin/ltlcross.cc: Also call determinize_unknown_acceptance() for
positive automata.
* tests/core/ltlcross3.test: Add another test case.
* NEWS: Mention the fix.

* doc/org/autcross.org, doc/org/autfilt.org, doc/org/citing.org,
doc/org/compile.org, doc/org/concepts.org, doc/org/csv.org,
doc/org/dstar2tgba.org, doc/org/genaut.org, doc/org/genltl.org,
doc/org/hierarchy.org, doc/org/hoa.org, doc/org/index.org,
doc/org/install.org, doc/org/ltl2tgba.org, doc/org/ltl2tgta.org,
doc/org/ltlcross.org, doc/org/ltlfilt.org, doc/org/ltlgrind.org,
doc/org/ltlsynt.org, doc/org/oaut.org, doc/org/randaut.org,
doc/org/randltl.org, doc/org/satmin.org, doc/org/tut.org,
doc/org/tut01.org, doc/org/tut02.org, doc/org/tut03.org,
doc/org/tut04.org, doc/org/tut10.org, doc/org/tut11.org,
doc/org/tut12.org, doc/org/tut20.org, doc/org/tut21.org,
doc/org/tut22.org, doc/org/tut23.org, doc/org/tut24.org,
doc/org/tut30.org, doc/org/tut31.org, doc/org/tut50.org,
doc/org/tut51.org, doc/org/tut52.org, doc/org/tut90.org,
doc/org/upgrade2.org: Run ispell-buffer on all these.
* bin/autfilt.cc, python/spot/__init__.py: Fix typos in
help texts noticed while spell-checking the org files.

* doc/org/.dir-locals.el.in, doc/org/init.el.in: Set the
SPOT_UNINSTALLED envvar, as we already do in the test suite.

Reported by Salomon Sickert.

* bin/ltlcross.cc: Also call determinize_unknown_acceptance() for
positive automata.
* tests/core/ltlcross3.test: Add another test case.
* NEWS: Mention the fix.

* configure.ac, NEWS, doc/org/setup.org: Set version to 2.9.2.

Fixes #420 reported by Salomon Sickert.

* bin/ltlcross.cc: Call determine_unknown_acceptance().
* spot/twaalgos/sccinfo.cc, spot/twaalgos/sccinfo.hh: Document
that one_accepting_scc()==-1 can mean "don't know", and update
determine_unknown_acceptance() to set one_acc_scc_.
* tests/core/ltlcross3.test: Add test case.
* NEWS: Mention the fixes.

* spot/tl/formula.hh (formula::operator bool): Mark as noexcept.
* bin/common_trans.hh, bin/common_trans.cc: Use std::atomic instead of
volatile.

Fixes #420 reported by Salomon Sickert.

* bin/ltlcross.cc: Call determine_unknown_acceptance().
* spot/twaalgos/sccinfo.cc, spot/twaalgos/sccinfo.hh: Document
that one_accepting_scc()==-1 can mean "don't know", and update
determine_unknown_acceptance() to set one_acc_scc_.
* tests/core/ltlcross3.test: Add test case.
* NEWS: Mention the fixes.

* configure.ac: Here.

* spot/tl/formula.hh (formula::operator bool): Make it explicit.  When
compiling in C++20 mode with g++ 10.1, this bool operator was used
instead of the comparison operators while looking up a
std::pair<formula,formula> in a hash map, causing many test suite
failures.  This problem does not occur with clang++ 10.0, so it
might just be a bug in g++ 10.1.  But having explicit operator bool
is good practice anyway.

With GCC 10.1 all comparisons that default to the <=> C++20 comparison
operator emit a spurious zero-as-null-pointer-constant warning, which
is an error in our configuration.  This is due to an implementation
choice in the libstdc++ library, so it also causes warning from
clang++ 10.0 when using the same libstdc++ library.  A fix for GCC
PR95242 was committed in g++ (not in libstdc++), so while g++ 10.2
might be fixed, clang++ will need a similar fix.

I've seen those failures on Arch linux with gcc 10.1.0-2 and clang
10.0.0-3.  On Debian sid, g++ 10.1.0-4 seems to already include the
fix.

* m4/gccwarn.m4: Include a string comparison in the test code so that
-Wzero-as-null-pointer-constant is not enabled if it would produce
warnings on such statements.

* spot/tl/formula.hh (formula::operator bool): Mark as noexcept.
* bin/common_trans.hh, bin/common_trans.cc: Use std::atomic instead of
volatile.

* configure.ac: Activate C++17, and replace --enable-c++17 by
--enable-c++20.

* configure.ac: Activate C++17, and replace --enable-c++17 by
--enable-c++20.
* NEWS: Mention the news.
* .gitlab-ci.yml: Use C++20 for the former C++17 builds.
* HACKING, README, doc/org/compile.org, doc/org/concepts.org,
doc/org/index.org, doc/org/install.org, doc/org/tut.org,
doc/org/upgrade2.org, spot/misc/escape.hh: Adjust mentions
of C++14.