* NEWS: Update.
* spot/tl/hierarchy.cc: Replace rabin_to_buchi_maybe() with
is_buchi_realizable().
* spot/twaalgos/remfin.cc: Implement it.
* spot/twaalgos/remfin.hh: Declare it.

* spot/tl/hierarchy.cc: Factorisations, improvements.
* spot/twaalgos/totgba.cc:  Typos.

* spot/tl/hierarchy.hh, spot/tl/hierarchy.cc (nesting_depth): New
function.
* python/spot/__init__.py: Also make it a method of formula in Python
* bin/common_output.cc, bin/common_output.hh: Implement
--stats=%[OP]n.
* NEWS: Mention it.
* tests/core/format.test, tests/python/formulas.ipynb: Test it.

* doc/footer.html: Make the footer XML compatible.
* doc/mainpage.dox: Fix references to modules.
* spot/tl/formula.hh: Introduce a hierarchy module.
* spot/tl/hierarchy.hh: Use it.

* spot/misc/bitvect.cc, spot/misc/bitvect.hh, spot/tl/formula.cc,
spot/tl/formula.hh: Here.
* NEWS: Mention the bug.

Fixes #306.

* spot/tl/formula.hh, python/spot/__init__.py: Implement this
in C++ and Python.
* doc/org/tut03.org: Document (and indirectly test) it.
* NEWS: Mention it.

Fixes #307.

* spot/tl/formula.hh: Here.
* tests/python/ltlparse.py: Test it.
* NEWS: Mention it.

* spot/tl/hierarchy.cc: Rewrite is_recurrence(), is_persistence()
* spot/tl/hierarchy.hh: Fix typo.
* tests/core/hierarchy.test: Add tests.

* spot/misc/bitvect.cc, spot/misc/bitvect.hh, spot/tl/formula.cc,
spot/tl/formula.hh: Here.
* NEWS: Mention the bug.

This is not optimal yet because it still construct a minimal WDBA
internally, but it's better than the previous way to call
minimize_obligation() since it can avoid constructing the minimized
automaton in a few more cases.

* spot/tl/hierarchy.cc, spot/tl/hierarchy.hh: Introduce
is_obligation().
* bin/ltlfilt.cc: Wire it to --obligation.
* spot/twaalgos/minimize.cc: Implement is_wdba_realizable(),
needed by the above.
* tests/core/obligation.test: Test it.
* bin/man/spot-x.x, NEWS: Document it.

* spot/tl/hierarchy.cc: code was actually reachable.

Fixes #293.

* spot/tl/simplify.cc: Test implications that would yield tt or ff
first.  In rules of the form "if a => b, a op b = b" also check
if b => a, and in this case return smallest(a,b).
* tests/core/reduccmp.test: Add a test.
* NEWS: Mention it.

Fixes #293.

* spot/tl/simplify.cc: Test implications that would yield tt or ff
first.  In rules of the form "if a => b, a op b = b" also check
if b => a, and in this case return smallest(a,b).
* tests/core/reduccmp.test: Add a test.
* NEWS: Mention it.

Fixes #285, reported by Florian Perlié-Long.

* NEWS: Mention the issue.
* spot/tl/formula.cc: Fix it.
* tests/core/kind.test: Document it.
* THANKS: Add Florian.

Fixes #285, reported by Florian Perlié-Long.

* NEWS: Mention the issue.
* spot/tl/formula.cc: Fix it.
* tests/core/kind.test: Document it.
* THANKS: Add Florian.

* NEWS: Update.
* bin/man/spot-x.x: Add environment variable.
* spot/tl/hierarchy.cc: Implement them.
* spot/tl/hierarchy.hh: Declare them.

* NEWS: Declare it.
* spot/tl/hierarchy.cc: Remove static keyword and anonymous namespace.
* spot/tl/hierarchy.hh: Declare function.

This addresses part of #35, and is just a generalization of the rules
from 646c5170 for #263 (hence, no new documentation).

* spot/tl/simplify.cc: Implement this.
* tests/core/reduccmp.test: Add test cases.
* tests/core/stutter-tgba.test: Adjust to expect smaller automata.

Fixes #108.

* spot/tl/simplify.cc: Implement the reduction.
* doc/tl/tl.tex, NEWS: Document it.
* tests/core/reduccmp.test: Test it.

For #263, reported by Mikuláš Klokočka.

G(a & Xe1 & F(b & e2)) = G(a & e1 & Fb & e2)
F(a | Xu1 | G(b | u2)) = F(a | u1 | Gb | u2)

* spot/tl/simplify.cc: Implement the rules.
* doc/tl/tl.tex, NEWS: Document them.
* tests/core/reduccmp.test, tests/core/eventuniv.test: Add test cases.
* tests/core/det.test, tests/core/ltl2tgba2.test: Adjust to expect
smaller automata.
* THANKS: Add Mikuláš.

* spot/tl/hierarchy.cc (is_recurrence): Do not request state-based
acceptance, now that the Rabin->DBA conversionn works on
transition-based acceptance as well.

* spot/tl/formula.hh: Move all throw statements behind
some [[noreturn]] report...() methods...
* spot/tl/formula.cc: ... defined here.  This makes the methods
shorter and helps their inlining.  Incidentally, this also removes the
uninitialized read that weirdly occurs when _GLIBCXX_DEBUG is on, as
observed with #184, but I do not know why.

The cache used in formula simplification will keep atomic propositions
defined between several translations, and may impact variable order.
Reported by Maximilien Colange.

* spot/tl/simplify.hh, spot/tl/simplify.cc,
spot/twaalgos/translate.cc, spot/twaalgos/translate.hh (clear_cache):
New method.
* bin/ltl2tgba.cc, bin/ltl2tgta.cc: Call it.
* spot/twaalgos/stats.cc: Do not keep a point to the formula after
printing statistics.
* tests/core/ltl2tgba.test: Add a test case.
* tests/core/readsave.test: Adjust one formula.
* NEWS: Mention the issue.

The cache used in formula simplification will keep atomic propositions
defined between several translations, and may impact variable order.
Reported by Maximilien Colange.

* spot/tl/simplify.hh, spot/tl/simplify.cc,
spot/twaalgos/translate.cc, spot/twaalgos/translate.hh (clear_cache):
New method.
* bin/ltl2tgba.cc, bin/ltl2tgta.cc: Call it.
* spot/twaalgos/stats.cc: Do not keep a point to the formula after
printing statistics.
* tests/core/ltl2tgba.test: Add a test case.
* tests/core/readsave.test: Adjust one formula.
* NEWS: Mention the issue.

Fixes #260.  Reported by František Blahoudek.

The simplification F(f)|q = F(f|q), where q designates an event_univ
formula, was not always applied because of a couple of issue: (1) the
mospliter was ignoring event_univ unless favor_event_univ was set, (2)
when processing formulas from res_EventUniv they were not put back
into res_F or res_G to be subject to the F/G rules.

* spot/tl/simplify.cc: Improve handling of the above points.
* tests/core/reduccmp.test: Adjust and add test case.
* tests/core/ltl2tgba2.test, tests/python/atva16-fig2a.ipynb: Adjust.

Fixes #260.  Reported by František Blahoudek.

The simplification F(f)|q = F(f|q), where q designates an event_univ
formula, was not always applied because of a couple of issue: (1) the
mospliter was ignoring event_univ unless favor_event_univ was set, (2)
when processing formulas from res_EventUniv they were not put back
into res_F or res_G to be subject to the F/G rules.

* spot/tl/simplify.cc: Improve handling of the above points.
* tests/core/reduccmp.test: Adjust and add test case.
* tests/core/ltl2tgba2.test, tests/python/atva16-fig2a.ipynb: Adjust.

For #212.

* spot/twa/twa.hh: Rename prop_deterministic() as prop_universal(),
and keep the old name as deprecated.
* spot/twaalgos/isdet.cc, spot/twaalgos/isdet.hh: Rename
is_deterministic() as is_universal(), and add a new function
for is_deterministic().
* doc/org/concepts.org, doc/org/hoa.org, doc/org/tut21.org,
spot/tl/hierarchy.cc, spot/twa/twagraph.cc,
spot/twaalgos/are_isomorphic.cc, spot/twaalgos/determinize.cc,
spot/twaalgos/dtbasat.cc, spot/twaalgos/dtwasat.cc,
spot/twaalgos/hoa.cc, spot/twaalgos/minimize.cc,
spot/twaalgos/postproc.cc, spot/twaalgos/product.cc,
spot/twaalgos/randomgraph.cc, spot/twaalgos/remfin.cc,
spot/twaalgos/simulation.cc, spot/twaalgos/totgba.cc,
spot/twaalgos/word.cc, tests/python/product.ipynb,
tests/python/remfin.py: Adjust.
* NEWS: Mention the change.

* spot/twa/twa.hh: Add support.  Make two constructors for prop_set in
order to diagnose constructions with 5 arguments.
* spot/parseaut/parseaut.yy: Adjust diagnostics for complete and
deterministic.
* spot/tl/exclusive.cc, spot/twa/twagraph.cc,
spot/twaalgos/alternation.cc, spot/twaalgos/complete.cc,
spot/twaalgos/complete.hh, spot/twaalgos/degen.cc,
spot/twaalgos/determinize.cc, spot/twaalgos/hoa.cc,
spot/twaalgos/isdet.cc, spot/twaalgos/mask.cc,
spot/twaalgos/minimize.cc, spot/twaalgos/product.cc,
spot/twaalgos/remfin.cc, spot/twaalgos/remprop.cc,
spot/twaalgos/sbacc.cc, spot/twaalgos/sccfilter.cc,
spot/twaalgos/simulation.cc, spot/twaalgos/strength.cc,
spot/twaalgos/stutter.cc, spot/twaalgos/totgba.cc,
tests/core/parseaut.test, tests/python/product.ipynb: Adjust.
* NEWS, doc/org/concepts.org, doc/org/hoa.org,
doc/org/tut21.org: Document it.

* bin/common_output.cc: Move some of the printing code...
* spot/tl/hierarchy.cc, spot/tl/hierarchy.hh: ... here, as new
  variants of mp_class...
* python/spot/impl.i: ... that we can now call from Python.
* python/ajax/spotcgi.in: Use those to simplify and extend
the code printing class membership.

* spot/twaalgos/minimize.cc (minimize_wdba): Diminish the color of
terminal SCCs that are incomplete, as if they had a non-accepting
sink as successor.
* spot/twaalgos/strength.hh, spot/twaalgos/strength.cc
(is_terminal_automaton): Add an option to ignore trivial SCC as we did
before, since it matters for deciding membership to the guarantee
class.
(is_safety_mwdba): Rewrite as ...
(is_safety_automaton): ... generalizating to any acceptance, and
ignoring trivial SCCs.
* bin/ltlfilt.cc, python/ajax/spotcgi.in, spot/tl/hierarchy.cc,
tests/core/ikwiad.cc: Adjust usage of is_terminal_automaton and
is_safety_automaton().
* tests/core/hierarchy.test: Add a problematic formula as test-case.
* NEWS: Mention the bug.

Tools for deciding the class of a formula.

* spot/tl/hierarchy.cc, spot/tl/hierarchy.hh: New files.
* spot/tl/Makefile.am: Add them.
* bin/common_output.cc, bin/common_output.hh: Implement --format=%h.
* tests/core/hierarchy.test: More tests.
* NEWS: Update.

Algorithms that remove transitions can turn a non-deterministic
automaton into a deterministic one, so we need to be able to specify
that determinism can be improved (as opposed to preserved).

* spot/twa/twa.hh (twa::prop_set::improve_det): New attribute.
(twa::prop_keep, twa::prop_copy): Honor it.
* spot/tl/exclusive.cc, spot/twaalgos/alternation.cc,
spot/twaalgos/complete.cc, spot/twaalgos/degen.cc,
spot/twaalgos/determinize.cc, spot/twaalgos/mask.cc,
spot/twaalgos/minimize.cc, spot/twaalgos/remfin.cc,
spot/twaalgos/remprop.cc, spot/twaalgos/sbacc.cc,
spot/twaalgos/sccfilter.cc, spot/twaalgos/simulation.cc,
spot/twaalgos/strength.cc, spot/twaalgos/stutter.cc,
spot/twaalgos/totgba.cc: Adjust calls to prop_keep() and
prop_copy().

Reported by Shufang Zhu.

* spot/tl/ltlf.cc, spot/tl/ltlf.hh: Fix the transltion
and update the comments.
* tests/core/ltlfilt.test: Adjust test cases.
* NEWS: Mention the fix.
* THANKS: Add Shufang Zhu.

Reported by Shufang Zhu.

* spot/tl/ltlf.cc, spot/tl/ltlf.hh: Fix the transltion
and update the comments.
* tests/core/ltlfilt.test: Adjust test cases.
* NEWS: Mention the fix.
* THANKS: Add Shufang Zhu.

* spot/graph/ngraph.hh, spot/ltsmin/ltsmin.cc,
spot/misc/bitvect.hh, spot/misc/intvcomp.cc,
spot/misc/satsolver.cc, spot/priv/weight.cc,
spot/ta/taexplicit.cc, spot/taalgos/minimize.cc,
spot/taalgos/reachiter.cc, spot/tl/exclusive.cc,
spot/tl/formula.cc, spot/tl/formula.hh,
spot/tl/mark.cc, spot/tl/mutation.cc,
spot/tl/relabel.cc, spot/tl/remove_x.cc,
spot/tl/simplify.cc, spot/twa/acc.cc,
spot/twa/acc.hh, spot/twa/formula2bdd.cc,
spot/twa/taatgba.cc, spot/twa/taatgba.hh,
spot/twa/twa.hh, spot/twa/twagraph.cc,
spot/twaalgos/bfssteps.cc, spot/twaalgos/canonicalize.cc,
spot/twaalgos/compsusp.cc, spot/twaalgos/copy.cc,
spot/twaalgos/cycles.cc, spot/twaalgos/degen.cc,
spot/twaalgos/determinize.cc, spot/twaalgos/dtwasat.cc,
spot/twaalgos/emptiness.cc, spot/twaalgos/gv04.cc,
spot/twaalgos/hoa.cc, spot/twaalgos/ltl2taa.cc,
spot/twaalgos/ltl2tgba_fm.cc, spot/twaalgos/magic.cc,
spot/twaalgos/mask.hh, spot/twaalgos/minimize.cc,
spot/twaalgos/powerset.cc, spot/twaalgos/product.cc,
spot/twaalgos/randomgraph.cc, spot/twaalgos/reachiter.cc,
spot/twaalgos/relabel.cc, spot/twaalgos/remfin.cc,
spot/twaalgos/sccfilter.cc, spot/twaalgos/se05.cc,
spot/twaalgos/simulation.cc, spot/twaalgos/stutter.cc,
spot/twaalgos/tau03opt.cc, spot/twaalgos/totgba.cc,
spot/twaalgos/word.cc, tests/core/bitvect.cc: here.

Fixes #187.

* spot/tl/ltlf.cc, spot/tl/ltlf.hh: New files.
* spot/tl/Makefile.am: Add them.
* bin/ltlfilt.cc: Add a new option.
* bin/man/ltlfilt.x: Add bibliographic reference.
* tests/core/ltlfilt.test: Add more tests.
* tests/python/ltlf.py: New file.
* tests/Makefile.am: Add it.
* python/spot/impl.i: Python bindings.
* NEWS: Mention it.

These were not actually printing in "SERE" mode due to a copy/paste
error.  PVS-Studio seems really good at finding those.  For #192.

* spot/tl/print.cc: Fix it.
* NEWS: Mention the bug.