288 lines
7.2 KiB
Org Mode
288 lines
7.2 KiB
Org Mode
# -*- coding: utf-8 -*-
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#+TITLE: Converting Rabin (or Other) to Büchi, and simplifying it
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#+SETUPFILE: setup.org
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#+HTML_LINK_UP: tut.html
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Consider the following Rabin automaton, generated by =ltl2dstar=:
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#+BEGIN_SRC sh :results verbatim :exports code
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ltldo ltl2dstar -f 'F(Xp1 xor XXp1)' -H > tut30.hoa
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#+END_SRC
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#+RESULTS:
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#+NAME: tut30in
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#+BEGIN_SRC sh :results verbatim :exports none
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autfilt tut30.hoa --dot=.a
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#+END_SRC
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#+RESULTS: tut30in
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#+begin_example
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digraph G {
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rankdir=LR
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label=<(Fin(<font color="#5DA5DA">â¿</font>) & Inf(<font color="#F17CB0">â¶</font>)) | (Fin(<font color="#FAA43A">â·</font>) & Inf(<font color="#B276B2">â¸</font>)) | (Fin(<font color="#60BD68">â¹</font>) & Inf(<font color="#F15854">âº</font>))>
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labelloc="t"
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node [shape="circle"]
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fontname="Lato"
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node [fontname="Lato"]
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edge [fontname="Lato"]
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node[style=filled, fillcolor="#ffffa0"] edge[arrowhead=vee, arrowsize=.7]
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I [label="", style=invis, width=0]
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I -> 6
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0 [label=<0<br/><font color="#FAA43A">â·</font><font color="#F15854">âº</font>>]
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0 -> 2 [label=<!p1>]
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0 -> 4 [label=<p1>]
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1 [label=<1<br/><font color="#FAA43A">â·</font><font color="#F15854">âº</font>>]
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1 -> 4 [label=<!p1>]
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1 -> 3 [label=<p1>]
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2 [label=<2<br/><font color="#B276B2">â¸</font><font color="#60BD68">â¹</font>>]
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2 -> 0 [label=<!p1>]
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2 -> 4 [label=<p1>]
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3 [label=<3<br/><font color="#B276B2">â¸</font><font color="#60BD68">â¹</font>>]
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3 -> 4 [label=<!p1>]
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3 -> 1 [label=<p1>]
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4 [label=<4<br/><font color="#F17CB0">â¶</font><font color="#FAA43A">â·</font><font color="#60BD68">â¹</font>>]
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4 -> 4 [label=<!p1>]
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4 -> 4 [label=<p1>]
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5 [label=<5<br/><font color="#FAA43A">â·</font><font color="#60BD68">â¹</font>>]
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5 -> 2 [label=<!p1>]
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5 -> 3 [label=<p1>]
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6 [label=<6<br/><font color="#FAA43A">â·</font><font color="#60BD68">â¹</font>>]
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6 -> 5 [label=<!p1>]
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6 -> 5 [label=<p1>]
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}
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#+end_example
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#+BEGIN_SRC dot :file tut30in.png :cmdline -Tpng :var txt=tut30in :exports results
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$txt
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#+END_SRC
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#+RESULTS:
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[[file:tut30in.png]]
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Our goal is to generate an equivalent Büchi automaton, preserving
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determinism if possible. However nothing of what we will write is
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specific to Rabin acceptance: the same code will convert automata with
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any acceptance to Büchi acceptance.
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* Shell
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We use =autfilt= with option =-B= to request Büchi acceptance and
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state-based output, =-D= to express a preference for deterministic
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output, and =-H= for output in the HOA format. Using option
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=-D/--deterministic= (or =--small=) actually activates the
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"postprocessing" routines of Spot: the acceptance will not only be
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changed to Büchi, but simplification routines (useless SCCs removal,
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simulation-based reductions, acceptance sets simplifications,
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WDBA-minimization, ...) will also be applied.
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#+BEGIN_SRC sh :results verbatim :exports both
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autfilt -B -D -H tut30.hoa
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#+END_SRC
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#+RESULTS:
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#+begin_example
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HOA: v1
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States: 5
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Start: 1
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AP: 1 "p1"
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acc-name: Buchi
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Acceptance: 1 Inf(0)
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properties: trans-labels explicit-labels state-acc complete
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properties: deterministic inherently-weak
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--BODY--
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State: 0 {0}
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[t] 0
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State: 1
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[t] 2
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State: 2
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[!0] 3
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[0] 4
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State: 3
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[0] 0
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[!0] 3
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State: 4
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[!0] 0
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[0] 4
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--END--
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#+end_example
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#+NAME: tut30out
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#+BEGIN_SRC sh :results verbatim :exports none
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autfilt -B -D tut30.hoa
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#+END_SRC
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#+RESULTS: tut30out
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#+begin_example
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digraph G {
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rankdir=LR
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node [shape="circle"]
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fontname="Lato"
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node [fontname="Lato"]
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edge [fontname="Lato"]
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node[style=filled, fillcolor="#ffffa0"] edge[arrowhead=vee, arrowsize=.7]
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I [label="", style=invis, width=0]
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I -> 1
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0 [label="0", peripheries=2]
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0 -> 0 [label=<1>]
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1 [label="1"]
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1 -> 2 [label=<1>]
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2 [label="2"]
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2 -> 3 [label=<!p1>]
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2 -> 4 [label=<p1>]
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3 [label="3"]
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3 -> 0 [label=<p1>]
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3 -> 3 [label=<!p1>]
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4 [label="4"]
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4 -> 0 [label=<!p1>]
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4 -> 4 [label=<p1>]
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}
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#+end_example
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#+BEGIN_SRC dot :file tut30out.png :cmdline -Tpng :var txt=tut30out :exports results
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$txt
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#+END_SRC
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#+RESULTS:
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[[file:tut30out.png]]
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In the general case transforming an automaton with a complex
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acceptance condition into a Büchi automaton can make the output
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bigger. However the postprocessing routines may manage to simplify
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the result further.
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* Python
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The Python version uses the =postprocess()= routine:
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#+BEGIN_SRC python :results output :exports both
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import spot
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aut = spot.automaton('tut30.hoa').postprocess('BA', 'deterministic')
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print(aut.to_str('hoa'))
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#+END_SRC
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#+RESULTS:
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#+begin_example
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HOA: v1
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States: 5
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Start: 1
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AP: 1 "p1"
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acc-name: Buchi
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Acceptance: 1 Inf(0)
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properties: trans-labels explicit-labels state-acc complete
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properties: deterministic inherently-weak
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--BODY--
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State: 0 {0}
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[t] 0
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State: 1
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[t] 2
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State: 2
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[!0] 3
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[0] 4
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State: 3
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[0] 0
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[!0] 3
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State: 4
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[!0] 0
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[0] 4
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--END--
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#+end_example
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The =postprocess()= function has an interface similar to
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[[file:tut10.org][the =translate()= function discussed previously]]:
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#+BEGIN_SRC python :results output :exports both
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import spot
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help(spot.postprocess)
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#+END_SRC
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#+RESULTS:
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#+begin_example
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Help on function postprocess in module spot:
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postprocess(automaton, *args)
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Post process an automaton.
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This applies a number of simlification algorithms, depending on
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the options supplied. Keep in mind that 'Deterministic' expresses
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just a preference that may not be satisfied if the input is
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not already 'Deterministic'.
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The optional arguments should be strings among the following:
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- at most one in 'Generic', 'TGBA', 'BA', or 'Monitor'
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(type of automaton to build)
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- at most one in 'Small', 'Deterministic', 'Any'
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(preferred characteristics of the produced automaton)
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- at most one in 'Low', 'Medium', 'High'
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(optimization level)
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- any combination of 'Complete' and 'StateBasedAcceptance'
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(or 'SBAcc' for short)
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The default corresponds to 'generic', 'small' and 'high'.
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#+end_example
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* C++
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The C++ version of this code is a bit more verbose, because the
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=postprocess()= function does not exist. You have to instantiate a
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=postprocessor= object, configure it, and then call it for each
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automaton to process.
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#+BEGIN_SRC C++ :results verbatim :exports both
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#include <iostream>
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#include "parseaut/public.hh"
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#include "twaalgos/postproc.hh"
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#include "twaalgos/hoa.hh"
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int main()
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{
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std::string input = "tut30.hoa";
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spot::parse_aut_error_list pel;
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spot::bdd_dict_ptr dict = spot::make_bdd_dict();
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spot::parsed_aut_ptr pa = parse_aut(input, pel, dict);
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if (spot::format_parse_aut_errors(std::cerr, input, pel))
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return 1;
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if (pa->aborted)
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{
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std::cerr << "--ABORT-- read\n";
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return 1;
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}
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spot::postprocessor post;
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post.set_type(spot::postprocessor::BA);
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post.set_pref(spot::postprocessor::Deterministic);
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post.set_level(spot::postprocessor::High);
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auto aut = post.run(pa->aut);
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spot::print_hoa(std::cout, aut) << '\n';
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return 0;
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}
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#+END_SRC
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#+RESULTS:
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#+begin_example
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HOA: v1
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States: 5
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Start: 1
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AP: 1 "p1"
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acc-name: Buchi
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Acceptance: 1 Inf(0)
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properties: trans-labels explicit-labels state-acc complete
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properties: deterministic inherently-weak
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--BODY--
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State: 0 {0}
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[t] 0
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State: 1
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[t] 2
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State: 2
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[!0] 3
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[0] 4
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State: 3
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[0] 0
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[!0] 3
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State: 4
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[!0] 0
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[0] 4
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--END--
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#+end_example
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