Add code example using the postprocessor.

* doc/org/tut30.org: New file.
* doc/Makefile.am, doc/org/tut.org: Add it.

doc/Makefile.am

@@ -91,6 +91,7 @@ ORG_FILES = \
   org/tut20.org \
   org/tut21.org \
   org/tut22.org \
+  org/tut30.org \
   org/satmin.org \
   org/satmin.tex \
   org/setup.org \

doc/org/tut.org

@@ -17,6 +17,7 @@ three interfaces supported by Spot: shell commands, Python, or C++.
 - [[file:tut02.org][Relabeling Formulas]]
 - [[file:tut10.org][Translating an LTL formula into a never claim]]
 - [[file:tut20.org][Converting a never claim into HOA]]
+- [[file:tut30.org][Converting Rabin (or Other) to Büchi, and simplifying it]]
 
 * Examples in Python and C++
 

doc/org/tut30.org

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