diff --git a/NEWS b/NEWS
index 23739d738..32a1b0f19 100644
--- a/NEWS
+++ b/NEWS
@@ -85,6 +85,11 @@ New in spot 2.10.6.dev  (not yet released)
   - complement() used to always turn tautological acceptance conditions
     into Büchi.  It now only does that if the automaton is modified.
 
+  - The zielonka_tree construction was optimized using the same
+    memoization trick that is used in ACD.  Additionally it can now be
+    run with additional option to abort when the tree as an unwanted
+    shape, or to turn the tree into a DAG.
+
 New in spot 2.10.6  (2022-05-18)
 
   Bugs fixed:
diff --git a/spot/twaalgos/zlktree.cc b/spot/twaalgos/zlktree.cc
index 2f87e6352..f31c46896 100644
--- a/spot/twaalgos/zlktree.cc
+++ b/spot/twaalgos/zlktree.cc
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2021 Laboratoire de Recherche et Developpement de
+// Copyright (C) 2021, 2022 Laboratoire de Recherche et Developpement de
 // l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -109,7 +109,8 @@ namespace spot
     }
   }
 
-  zielonka_tree::zielonka_tree(const acc_cond& cond)
+  zielonka_tree::zielonka_tree(const acc_cond& cond,
+                               zielonka_tree_options opt)
   {
     const acc_cond::acc_code& code = cond.get_acceptance();
     auto all = cond.all_sets();
@@ -120,11 +121,47 @@ namespace spot
     nodes_[0].colors = all;
     nodes_[0].level = 0;
 
+    robin_hood::unordered_node_map<acc_cond::mark_t, unsigned> nmap;
+
     std::vector<size_model> models;
     // This loop is a BFS over the increasing set of nodes.
     for (unsigned node = 0; node < nodes_.size(); ++node)
     {
       acc_cond::mark_t colors = nodes_[node].colors;
+      unsigned nextlvl = nodes_[node].level + 1;
+
+      // Have we already seen this combination of colors previously?
+      // If yes, simply copy the children.
+      if (auto p = nmap.emplace(colors, node); !p.second)
+        {
+          unsigned fc = nodes_[p.first->second].first_child;
+          if (!fc)              // this is a leaf
+            {
+              ++num_branches_;
+              continue;
+            }
+          if (!!(opt & zielonka_tree_options::MERGE_SUBTREES))
+            {
+              nodes_[node].first_child = fc;
+              continue;
+            }
+          unsigned child = fc;
+          unsigned first = nodes_.size();
+          nodes_[node].first_child = first;
+          do
+            {
+              auto& c = nodes_[child];
+              child = c.next_sibling;
+              nodes_.push_back({node, static_cast<unsigned>(nodes_.size() + 1),
+                                0, nextlvl, c.colors});
+            }
+          while (child != fc);
+          nodes_.back().next_sibling = first;
+          // We do not have to test the shape since this is the second time
+          // we see these colors;
+          continue;
+        }
+
       bool is_accepting = code.accepting(colors);
       if (node == 0)
         is_even_ = is_accepting;
@@ -145,15 +182,32 @@ namespace spot
       nodes_.reserve(first + num_children);
       for (auto& m: models)
         nodes_.push_back({node, static_cast<unsigned>(nodes_.size() + 1),
-                          0, nodes_[node].level + 1, m.model});
+                          0, nextlvl, m.model});
       nodes_.back().next_sibling = first;
 
       if (num_children > 1)
         {
+          bool abort = false;
           if (is_accepting)
-            has_rabin_shape_ = false;
+            {
+              has_rabin_shape_ = false;
+              if (!!(opt & zielonka_tree_options::ABORT_WRONG_SHAPE)
+                  && !!(opt & zielonka_tree_options::CHECK_RABIN))
+                abort = true;
+            }
           else
-            has_streett_shape_ = false;
+            {
+              has_streett_shape_ = false;
+              if (!!(opt & zielonka_tree_options::ABORT_WRONG_SHAPE)
+                  && !!(opt & zielonka_tree_options::CHECK_STREETT))
+                abort = true;
+            }
+          if (abort)
+            {
+              nodes_.clear();
+              num_branches_ = 0;
+              return;
+            }
         }
     }
 
@@ -523,14 +577,18 @@ namespace spot
           do
             {
               auto& c = nodes_[child];
+              // We have to read anything we need from C
+              // before emplace_back, which may reallocate.
+              acc_cond::mark_t colors = c.colors;
+              unsigned minstate = c.minstate;
+              child = c.next_sibling;
               nodes_.emplace_back(c.edges, c.states);
               auto& n = nodes_.back();
               n.parent = node;
               n.level = lvl + 1;
               n.scc = ref.scc;
-              n.colors = c.colors;
-              n.minstate = c.minstate;
-              child = c.next_sibling;
+              n.colors = colors;
+              n.minstate = minstate;
             }
           while (child != fc);
           chain_children(node, before, nodes_.size());
diff --git a/spot/twaalgos/zlktree.hh b/spot/twaalgos/zlktree.hh
index 675224682..b8e47bc2a 100644
--- a/spot/twaalgos/zlktree.hh
+++ b/spot/twaalgos/zlktree.hh
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2021 Laboratoire de Recherche et Developpement de
+// Copyright (C) 2021, 2022 Laboratoire de Recherche et Developpement de
 // l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -28,6 +28,68 @@
 
 namespace spot
 {
+  /// \ingroup twa_acc_transform
+  /// \brief Options to alter the behavior of acd
+  enum class zielonka_tree_options
+  {
+    /// Build the ZlkTree, without checking its shape.
+    NONE = 0,
+    /// Check if the ZlkTree has Rabin shape.
+    /// This actually has no effect unless ABORT_WRONG_SHAPE is set,
+    /// because zielonka_tree always check the shape.
+    CHECK_RABIN = 1,
+    /// Check if the ZlkTree has Streett shape.
+    /// This actually has no effect unless ABORT_WRONG_SHAPE is set,
+    /// because zielonka_tree always check the shape.
+    CHECK_STREETT = 2,
+    /// Check if the ZlkTree has Parity shape
+    /// This actually has no effect unless ABORT_WRONG_SHAPE is set,
+    /// because zielonka_tree always check the shape.
+    CHECK_PARITY = CHECK_RABIN | CHECK_STREETT,
+    /// Abort the construction of the ZlkTree if it does not have the
+    /// shape that is tested.  When that happens, num_branches() is set
+    /// to 0.
+    ABORT_WRONG_SHAPE = 4,
+    /// Fuse identical substree.  This cannot be used with
+    /// zielonka_tree_transform().  However it saves memory if the
+    /// only use of the zielonka_tree to check the shape.
+    MERGE_SUBTREES = 8,
+  };
+
+#ifndef SWIG
+  inline
+  bool operator!(zielonka_tree_options me)
+  {
+    return me == zielonka_tree_options::NONE;
+  }
+
+  inline
+  zielonka_tree_options operator&(zielonka_tree_options left,
+                                  zielonka_tree_options right)
+  {
+    typedef std::underlying_type_t<zielonka_tree_options> ut;
+    return static_cast<zielonka_tree_options>(static_cast<ut>(left)
+                                              & static_cast<ut>(right));
+  }
+
+  inline
+  zielonka_tree_options operator|(zielonka_tree_options left,
+                                  zielonka_tree_options right)
+  {
+    typedef std::underlying_type_t<zielonka_tree_options> ut;
+    return static_cast<zielonka_tree_options>(static_cast<ut>(left)
+                                              | static_cast<ut>(right));
+  }
+
+  inline
+  zielonka_tree_options operator-(zielonka_tree_options left,
+                                  zielonka_tree_options right)
+  {
+    typedef std::underlying_type_t<zielonka_tree_options> ut;
+    return static_cast<zielonka_tree_options>(static_cast<ut>(left)
+                                              & ~static_cast<ut>(right));
+  }
+#endif
   /// \ingroup twa_acc_transform
   /// \brief Zielonka Tree implementation
   ///
@@ -41,7 +103,8 @@ namespace spot
   {
   public:
     /// \brief Build a Zielonka tree from the acceptance condition.
-    zielonka_tree(const acc_cond& cond);
+    zielonka_tree(const acc_cond& cond,
+                  zielonka_tree_options opt = zielonka_tree_options::NONE);
 
     /// \brief The number of branches in the Zielonka tree.
     ///
diff --git a/tests/python/zlktree.ipynb b/tests/python/zlktree.ipynb
index d46e2ce2c..ae44ad37d 100644
--- a/tests/python/zlktree.ipynb
+++ b/tests/python/zlktree.ipynb
@@ -216,7 +216,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f0c504752a0> >"
+       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f14702729c0> >"
       ]
      },
      "execution_count": 2,
@@ -640,7 +640,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c49328600> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f14701b7510> >"
       ]
      },
      "execution_count": 10,
@@ -1063,7 +1063,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c493284b0> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1470220960> >"
       ]
      },
      "execution_count": 11,
@@ -1256,7 +1256,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c49328f30> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f14701b75d0> >"
       ]
      },
      "execution_count": 13,
@@ -1701,7 +1701,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c49330420> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1470142240> >"
       ]
      },
      "execution_count": 14,
@@ -2096,7 +2096,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f0c493357e0> >"
+       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f147014b780> >"
       ]
      },
      "metadata": {},
@@ -2427,7 +2427,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f0c493357b0> >"
+       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f147014b750> >"
       ]
      },
      "metadata": {},
@@ -2513,7 +2513,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f0c49335390> >"
+       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f147014b1e0> >"
       ]
      },
      "metadata": {},
@@ -2624,7 +2624,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f0c49335420> >"
+       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f147014b2a0> >"
       ]
      },
      "metadata": {},
@@ -2662,7 +2662,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f0c49335360> >"
+       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f147014b150> >"
       ]
      },
      "metadata": {},
@@ -2700,7 +2700,7 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f0c493357b0> >"
+       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f147014b2d0> >"
       ]
      },
      "metadata": {},
@@ -2717,6 +2717,237 @@
     "    display(tcond)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "77db26c3",
+   "metadata": {},
+   "source": [
+    "## `zielonka_tree_options`\n",
+    "\n",
+    "The `zielonka_tree` class accepts a few options that can alter its behaviour.\n",
+    "\n",
+    "Options `CHECK_RABIN`, `CHECK_STREETT`, `CHECK_PARITY` can be combined with\n",
+    "`ABORT_WRONG_SHAPE` to abort the construction as soon as it is detected that the Zielonka tree has the wrong shape.  When this happens, the number of branchs of the tree is set to 0.\n",
+    "\n",
+    "For instance we can check that the original acceptance condition does not behaves like a Parity condition."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 17,
+   "id": "4fa47daf",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "(4, (Fin(0) & Inf(1) & (Inf(2) | Fin(3))) | ((Inf(0) | Fin(1)) & Fin(2) & Inf(3)))\n",
+      "0\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(c)\n",
+    "z = spot.zielonka_tree(c, spot.zielonka_tree_options_ABORT_WRONG_SHAPE \n",
+    "                          | spot.zielonka_tree_options_CHECK_PARITY)\n",
+    "print(z.num_branches())"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "4786f64c",
+   "metadata": {},
+   "source": [
+    "Option `MERGE_SUBTREE` will fuse identical nodes, turning the tree into a DAG.  (Actually, because this tree is stored as a left-child right-sibling tree, only the children of identical nodes are merged.):"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 18,
+   "id": "bc826090",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "image/svg+xml": [
+       "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n",
+       "<!DOCTYPE svg PUBLIC \"-//W3C//DTD SVG 1.1//EN\"\n",
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+       "<!-- 1&#45;&gt;4 -->\n",
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+      ],
+      "text/plain": [
+       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f147014bd20> >"
+      ]
+     },
+     "execution_count": 18,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "spot.zielonka_tree(c, spot.zielonka_tree_options_MERGE_SUBTREES)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "9d7688b3",
+   "metadata": {},
+   "source": [
+    "Such a DAG cannot be used by `zielonka_tree_transform()`, but it saves memory if we are only checking the shape of the tree/DAG."
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "75838579",
@@ -2731,7 +2962,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 19,
    "id": "ea3488b1",
    "metadata": {},
    "outputs": [],
@@ -2763,7 +2994,7 @@
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   {
    "cell_type": "code",
-   "execution_count": 18,
+   "execution_count": 20,
    "id": "fad721c0",
    "metadata": {},
    "outputs": [
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       "text/plain": [
-       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f0c49330f90> >"
+       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f1470142d50> >"
       ]
      },
-     "execution_count": 18,
+     "execution_count": 20,
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@@ -3886,7 +4117,7 @@
   },
   {
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-   "execution_count": 19,
+   "execution_count": 21,
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    "metadata": {},
    "outputs": [
@@ -3896,7 +4127,7 @@
        "False"
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-     "execution_count": 19,
+     "execution_count": 21,
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@@ -3932,7 +4163,7 @@
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-   "execution_count": 20,
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    "outputs": [
@@ -3942,7 +4173,7 @@
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-     "execution_count": 20,
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@@ -3953,7 +4184,7 @@
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@@ -3963,7 +4194,7 @@
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@@ -3984,7 +4215,7 @@
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@@ -3994,7 +4225,7 @@
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@@ -4005,7 +4236,7 @@
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@@ -4015,7 +4246,7 @@
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@@ -4026,7 +4257,7 @@
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@@ -4036,7 +4267,7 @@
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@@ -4047,7 +4278,7 @@
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@@ -4057,7 +4288,7 @@
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@@ -4094,7 +4325,7 @@
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@@ -4104,7 +4335,7 @@
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@@ -4131,7 +4362,7 @@
   },
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@@ -4737,10 +4968,10 @@
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+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f14701670f0> >"
       ]
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-     "execution_count": 27,
+     "execution_count": 29,
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@@ -4761,7 +4992,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 28,
+   "execution_count": 30,
    "id": "numerical-education",
    "metadata": {},
    "outputs": [
@@ -4771,7 +5002,7 @@
        "True"
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      },
-     "execution_count": 28,
+     "execution_count": 30,
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@@ -4790,7 +5021,7 @@
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@@ -5376,10 +5607,10 @@
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+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1470167210> >"
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-     "execution_count": 29,
+     "execution_count": 31,
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@@ -5401,7 +5632,7 @@
   },
   {
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+   "execution_count": 32,
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    "metadata": {},
    "outputs": [
@@ -5411,7 +5642,7 @@
        "15"
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@@ -5422,7 +5653,7 @@
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@@ -5432,7 +5663,7 @@
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@@ -5461,7 +5692,7 @@
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@@ -5471,7 +5702,7 @@
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@@ -5505,7 +5736,7 @@
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@@ -5523,7 +5754,7 @@
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@@ -5533,7 +5764,7 @@
   },
   {
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@@ -5564,7 +5795,7 @@
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@@ -5574,7 +5805,7 @@
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-   "execution_count": 38,
+   "execution_count": 40,
    "id": "813d15ed",
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@@ -6673,10 +6904,10 @@
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#N0\").click(function(){acd1_node(0, 0);});$(\"#acd1 #N1\").click(function(){acd1_node(1, 1);});$(\"#acd1 #N2\").click(function(){acd1_node(2, 1);});$(\"#acd1 #N3\").click(function(){acd1_node(3, 1);});$(\"#acd1 #N4\").click(function(){acd1_node(4, 1);});$(\"#acd1 #N5\").click(function(){acd1_node(5, 1);});$(\"#acd1 #N6\").click(function(){acd1_node(6, 1);});$(\"#acd1 #N7\").click(function(){acd1_node(7, 1);});$(\"#acd1 #N8\").click(function(){acd1_node(8, 1);});$(\"#acd1 #N9\").click(function(){acd1_node(9, 0);});$(\"#acd1 #N10\").click(function(){acd1_node(10, 0);});$(\"#acd1 #N11\").click(function(){acd1_node(11, 0);});$(\"#acd1 #N12\").click(function(){acd1_node(12, 0);});$(\"#acd1 #N13\").click(function(){acd1_node(13, 0);});$(\"#acd1 #N14\").click(function(){acd1_node(14, 0);});</script>"
       ],
       "text/plain": [
-       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f0c493420f0> >"
+       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f147016f1e0> >"
       ]
      },
-     "execution_count": 38,
+     "execution_count": 40,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -6695,7 +6926,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 39,
+   "execution_count": 41,
    "id": "00acde97",
    "metadata": {},
    "outputs": [
@@ -6705,7 +6936,7 @@
        "4"
       ]
      },
-     "execution_count": 39,
+     "execution_count": 41,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -6716,7 +6947,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 40,
+   "execution_count": 42,
    "id": "23c5f4df",
    "metadata": {},
    "outputs": [
@@ -6726,7 +6957,7 @@
        "8"
       ]
      },
-     "execution_count": 40,
+     "execution_count": 42,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -6737,7 +6968,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 41,
+   "execution_count": 43,
    "id": "da0bbcbe",
    "metadata": {},
    "outputs": [
@@ -6747,7 +6978,7 @@
        "0"
       ]
      },
-     "execution_count": 41,
+     "execution_count": 43,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -6758,7 +6989,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 42,
+   "execution_count": 44,
    "id": "da0dc5bc",
    "metadata": {},
    "outputs": [
@@ -6768,7 +6999,7 @@
        "8"
       ]
      },
-     "execution_count": 42,
+     "execution_count": 44,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -6788,7 +7019,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 43,
+   "execution_count": 45,
    "id": "94999c2e",
    "metadata": {},
    "outputs": [
@@ -7586,10 +7817,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c49342570> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f14700fe1e0> >"
       ]
      },
-     "execution_count": 43,
+     "execution_count": 45,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -7611,7 +7842,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 44,
+   "execution_count": 46,
    "id": "b57476cf",
    "metadata": {},
    "outputs": [
@@ -7640,7 +7871,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 45,
+   "execution_count": 47,
    "id": "f082b433",
    "metadata": {},
    "outputs": [
@@ -7912,10 +8143,10 @@
        "};$(\"#acdaut2 #E1\").addClass(\"acdN0\");$(\"#acdaut2 #E2\").addClass(\"acdN0\");$(\"#acdaut2 #E3\").addClass(\"acdN0\");$(\"#acdaut2 #E4\").addClass(\"acdN0\");$(\"#acdaut2 #E5\").addClass(\"acdN0\");$(\"#acdaut2 #E6\").addClass(\"acdN0\");$(\"#acdaut2 #E2\").addClass(\"acdN1\");$(\"#acdaut2 #E3\").addClass(\"acdN1\");$(\"#acdaut2 #E4\").addClass(\"acdN1\");$(\"#acdaut2 #E5\").addClass(\"acdN1\");$(\"#acdaut2 #E6\").addClass(\"acdN1\");$(\"#acdaut2 #E1\").addClass(\"acdN2\");$(\"#acdaut2 #E2\").addClass(\"acdN2\");$(\"#acdaut2 #E4\").addClass(\"acdN2\");$(\"#acdaut2 #E6\").addClass(\"acdN2\");$(\"#acdaut2 #E1\").click(function(){acd2_edge(1);});$(\"#acdaut2 #E2\").click(function(){acd2_edge(2);});$(\"#acdaut2 #E3\").click(function(){acd2_edge(3);});$(\"#acdaut2 #E4\").click(function(){acd2_edge(4);});$(\"#acdaut2 #E5\").click(function(){acd2_edge(5);});$(\"#acdaut2 #E6\").click(function(){acd2_edge(6);});$(\"#acdaut2 #S0\").click(function(){acd2_state(0);});$(\"#acdaut2 #S1\").click(function(){acd2_state(1);});$(\"#acdaut2 #S2\").click(function(){acd2_state(2);});$(\"#acd2 #N0\").click(function(){acd2_node(0, 1);});$(\"#acd2 #N1\").click(function(){acd2_node(1, 0);});$(\"#acd2 #N2\").click(function(){acd2_node(2, 0);});</script>"
       ],
       "text/plain": [
-       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f0c49342ea0> >"
+       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f14700fe300> >"
       ]
      },
-     "execution_count": 45,
+     "execution_count": 47,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -7931,7 +8162,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 46,
+   "execution_count": 48,
    "id": "597185c0",
    "metadata": {},
    "outputs": [
@@ -7944,11 +8175,11 @@
        "<!-- Generated by graphviz version 2.43.0 (0)\n",
        " -->\n",
        "<!-- Pages: 1 -->\n",
-       "<svg width=\"618pt\" height=\"267pt\"\n",
-       " viewBox=\"0.00 0.00 617.77 266.80\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n",
-       "<g id=\"graph0\" class=\"graph\" transform=\"scale(1.0 1.0) rotate(0) translate(4 262.8)\">\n",
-       "<polygon fill=\"white\" stroke=\"transparent\" points=\"-4,4 -4,-262.8 613.77,-262.8 613.77,4 -4,4\"/>\n",
-       "<text text-anchor=\"start\" x=\"283.39\" y=\"-228.6\" font-family=\"Lato\" font-size=\"14.00\">[Büchi]</text>\n",
+       "<svg width=\"618pt\" height=\"250pt\"\n",
+       " viewBox=\"0.00 0.00 617.77 250.00\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n",
+       "<g id=\"graph0\" class=\"graph\" transform=\"scale(1.0 1.0) rotate(0) translate(4 246)\">\n",
+       "<polygon fill=\"white\" stroke=\"transparent\" points=\"-4,4 -4,-246 613.77,-246 613.77,4 -4,4\"/>\n",
+       "<text text-anchor=\"start\" x=\"283.39\" y=\"-226.8\" font-family=\"Lato\" font-size=\"14.00\">[Büchi]</text>\n",
        "<!-- I -->\n",
        "<!-- 0 -->\n",
        "<g id=\"node2\" class=\"node\">\n",
@@ -8122,10 +8353,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480e0690> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f14700feb40> >"
       ]
      },
-     "execution_count": 46,
+     "execution_count": 48,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -8154,7 +8385,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 47,
+   "execution_count": 49,
    "id": "a4fd4105",
    "metadata": {},
    "outputs": [
@@ -8426,10 +8657,10 @@
        "};$(\"#acdaut3 #E1\").addClass(\"acdN0\");$(\"#acdaut3 #E2\").addClass(\"acdN0\");$(\"#acdaut3 #E3\").addClass(\"acdN0\");$(\"#acdaut3 #E4\").addClass(\"acdN0\");$(\"#acdaut3 #E5\").addClass(\"acdN0\");$(\"#acdaut3 #E6\").addClass(\"acdN0\");$(\"#acdaut3 #E1\").addClass(\"acdN1\");$(\"#acdaut3 #E2\").addClass(\"acdN1\");$(\"#acdaut3 #E4\").addClass(\"acdN1\");$(\"#acdaut3 #E6\").addClass(\"acdN1\");$(\"#acdaut3 #E2\").addClass(\"acdN2\");$(\"#acdaut3 #E3\").addClass(\"acdN2\");$(\"#acdaut3 #E4\").addClass(\"acdN2\");$(\"#acdaut3 #E5\").addClass(\"acdN2\");$(\"#acdaut3 #E6\").addClass(\"acdN2\");$(\"#acdaut3 #E1\").click(function(){acd3_edge(1);});$(\"#acdaut3 #E2\").click(function(){acd3_edge(2);});$(\"#acdaut3 #E3\").click(function(){acd3_edge(3);});$(\"#acdaut3 #E4\").click(function(){acd3_edge(4);});$(\"#acdaut3 #E5\").click(function(){acd3_edge(5);});$(\"#acdaut3 #E6\").click(function(){acd3_edge(6);});$(\"#acdaut3 #S0\").click(function(){acd3_state(0);});$(\"#acdaut3 #S1\").click(function(){acd3_state(1);});$(\"#acdaut3 #S2\").click(function(){acd3_state(2);});$(\"#acd3 #N0\").click(function(){acd3_node(0, 1);});$(\"#acd3 #N1\").click(function(){acd3_node(1, 0);});$(\"#acd3 #N2\").click(function(){acd3_node(2, 0);});</script>"
       ],
       "text/plain": [
-       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f0c480e05d0> >"
+       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f14700fed50> >"
       ]
      },
-     "execution_count": 47,
+     "execution_count": 49,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -8440,7 +8671,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 48,
+   "execution_count": 50,
    "id": "1a68f96a",
    "metadata": {},
    "outputs": [
@@ -8453,11 +8684,11 @@
        "<!-- Generated by graphviz version 2.43.0 (0)\n",
        " -->\n",
        "<!-- Pages: 1 -->\n",
-       "<svg width=\"606pt\" height=\"247pt\"\n",
-       " viewBox=\"0.00 0.00 605.77 246.80\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n",
-       "<g id=\"graph0\" class=\"graph\" transform=\"scale(1.0 1.0) rotate(0) translate(4 242.8)\">\n",
-       "<polygon fill=\"white\" stroke=\"transparent\" points=\"-4,4 -4,-242.8 601.77,-242.8 601.77,4 -4,4\"/>\n",
-       "<text text-anchor=\"start\" x=\"277.39\" y=\"-208.6\" font-family=\"Lato\" font-size=\"14.00\">[Büchi]</text>\n",
+       "<svg width=\"606pt\" height=\"230pt\"\n",
+       " viewBox=\"0.00 0.00 605.77 230.00\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n",
+       "<g id=\"graph0\" class=\"graph\" transform=\"scale(1.0 1.0) rotate(0) translate(4 226)\">\n",
+       "<polygon fill=\"white\" stroke=\"transparent\" points=\"-4,4 -4,-226 601.77,-226 601.77,4 -4,4\"/>\n",
+       "<text text-anchor=\"start\" x=\"277.39\" y=\"-206.8\" font-family=\"Lato\" font-size=\"14.00\">[Büchi]</text>\n",
        "<!-- I -->\n",
        "<!-- 0 -->\n",
        "<g id=\"node2\" class=\"node\">\n",
@@ -8610,10 +8841,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480e0de0> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f14700fea80> >"
       ]
      },
-     "execution_count": 48,
+     "execution_count": 50,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -8636,7 +8867,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 49,
+   "execution_count": 51,
    "id": "criminal-northwest",
    "metadata": {},
    "outputs": [
@@ -8762,10 +8993,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480e21e0> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1470107240> >"
       ]
      },
-     "execution_count": 49,
+     "execution_count": 51,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -8796,7 +9027,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 50,
+   "execution_count": 52,
    "id": "63c7c062",
    "metadata": {},
    "outputs": [
@@ -8874,10 +9105,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f0c480e22a0> >"
+       "<spot.zielonka_tree; proxy of <Swig Object of type 'spot::zielonka_tree *' at 0x7f1470107090> >"
       ]
      },
-     "execution_count": 50,
+     "execution_count": 52,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -8888,7 +9119,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 51,
+   "execution_count": 53,
    "id": "balanced-investing",
    "metadata": {},
    "outputs": [
@@ -9040,10 +9271,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480e2360> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1470107030> >"
       ]
      },
-     "execution_count": 51,
+     "execution_count": 53,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -9054,7 +9285,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 52,
+   "execution_count": 54,
    "id": "nutritional-rugby",
    "metadata": {},
    "outputs": [],
@@ -9064,7 +9295,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 53,
+   "execution_count": 55,
    "id": "criminal-marking",
    "metadata": {},
    "outputs": [
@@ -9333,10 +9564,10 @@
        "};$(\"#acdaut4 #E1\").addClass(\"acdN0\");$(\"#acdaut4 #E2\").addClass(\"acdN0\");$(\"#acdaut4 #E3\").addClass(\"acdN0\");$(\"#acdaut4 #E4\").addClass(\"acdN0\");$(\"#acdaut4 #E5\").addClass(\"acdN0\");$(\"#acdaut4 #E6\").addClass(\"acdN0\");$(\"#acdaut4 #E7\").addClass(\"acdN0\");$(\"#acdaut4 #E8\").addClass(\"acdN0\");$(\"#acdaut4 #E6\").addClass(\"acdN1\");$(\"#acdaut4 #E1\").click(function(){acd4_edge(1);});$(\"#acdaut4 #E2\").click(function(){acd4_edge(2);});$(\"#acdaut4 #E3\").click(function(){acd4_edge(3);});$(\"#acdaut4 #E4\").click(function(){acd4_edge(4);});$(\"#acdaut4 #E5\").click(function(){acd4_edge(5);});$(\"#acdaut4 #E6\").click(function(){acd4_edge(6);});$(\"#acdaut4 #E7\").click(function(){acd4_edge(7);});$(\"#acdaut4 #E8\").click(function(){acd4_edge(8);});$(\"#acdaut4 #S0\").click(function(){acd4_state(0);});$(\"#acdaut4 #S1\").click(function(){acd4_state(1);});$(\"#acd4 #N0\").click(function(){acd4_node(0, 1);});$(\"#acd4 #N1\").click(function(){acd4_node(1, 0);});</script>"
       ],
       "text/plain": [
-       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f0c480e2480> >"
+       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f1470107420> >"
       ]
      },
-     "execution_count": 53,
+     "execution_count": 55,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -9347,7 +9578,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 54,
+   "execution_count": 56,
    "id": "e7760d51",
    "metadata": {},
    "outputs": [
@@ -9357,7 +9588,7 @@
        "0"
       ]
      },
-     "execution_count": 54,
+     "execution_count": 56,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -9368,7 +9599,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 55,
+   "execution_count": 57,
    "id": "unusual-dependence",
    "metadata": {
     "scrolled": true
@@ -9477,10 +9708,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480e2d50> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1470107b70> >"
       ]
      },
-     "execution_count": 55,
+     "execution_count": 57,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -9491,7 +9722,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 56,
+   "execution_count": 58,
    "id": "d5440de1",
    "metadata": {},
    "outputs": [
@@ -9504,11 +9735,11 @@
        "<!-- Generated by graphviz version 2.43.0 (0)\n",
        " -->\n",
        "<!-- Pages: 1 -->\n",
-       "<svg width=\"378pt\" height=\"177pt\"\n",
-       " viewBox=\"0.00 0.00 377.50 176.62\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n",
-       "<g id=\"graph0\" class=\"graph\" transform=\"scale(1.0 1.0) rotate(0) translate(4 172.62)\">\n",
-       "<polygon fill=\"white\" stroke=\"transparent\" points=\"-4,4 -4,-172.62 373.5,-172.62 373.5,4 -4,4\"/>\n",
-       "<text text-anchor=\"start\" x=\"163.25\" y=\"-138.42\" font-family=\"Lato\" font-size=\"14.00\">[Büchi]</text>\n",
+       "<svg width=\"378pt\" height=\"160pt\"\n",
+       " viewBox=\"0.00 0.00 377.50 159.82\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n",
+       "<g id=\"graph0\" class=\"graph\" transform=\"scale(1.0 1.0) rotate(0) translate(4 155.82)\">\n",
+       "<polygon fill=\"white\" stroke=\"transparent\" points=\"-4,4 -4,-155.82 373.5,-155.82 373.5,4 -4,4\"/>\n",
+       "<text text-anchor=\"start\" x=\"163.25\" y=\"-136.62\" font-family=\"Lato\" font-size=\"14.00\">[Büchi]</text>\n",
        "<!-- I -->\n",
        "<!-- 0 -->\n",
        "<g id=\"node2\" class=\"node\">\n",
@@ -9624,10 +9855,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480ea150> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f147010d240> >"
       ]
      },
-     "execution_count": 56,
+     "execution_count": 58,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -9638,7 +9869,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 57,
+   "execution_count": 59,
    "id": "9ed0bc59",
    "metadata": {},
    "outputs": [],
@@ -9658,7 +9889,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 58,
+   "execution_count": 60,
    "id": "deb92971",
    "metadata": {},
    "outputs": [
@@ -9963,10 +10194,10 @@
        "};$(\"#acdaut5 #E1\").addClass(\"acdN0\");$(\"#acdaut5 #E2\").addClass(\"acdN0\");$(\"#acdaut5 #E3\").addClass(\"acdN0\");$(\"#acdaut5 #E4\").addClass(\"acdN0\");$(\"#acdaut5 #E5\").addClass(\"acdN0\");$(\"#acdaut5 #E6\").addClass(\"acdN0\");$(\"#acdaut5 #E7\").addClass(\"acdN0\");$(\"#acdaut5 #E1\").addClass(\"acdN1\");$(\"#acdaut5 #E3\").addClass(\"acdN1\");$(\"#acdaut5 #E4\").addClass(\"acdN1\");$(\"#acdaut5 #E5\").addClass(\"acdN1\");$(\"#acdaut5 #E7\").addClass(\"acdN2\");$(\"#acdaut5 #E1\").click(function(){acd5_edge(1);});$(\"#acdaut5 #E2\").click(function(){acd5_edge(2);});$(\"#acdaut5 #E3\").click(function(){acd5_edge(3);});$(\"#acdaut5 #E4\").click(function(){acd5_edge(4);});$(\"#acdaut5 #E5\").click(function(){acd5_edge(5);});$(\"#acdaut5 #E6\").click(function(){acd5_edge(6);});$(\"#acdaut5 #E7\").click(function(){acd5_edge(7);});$(\"#acdaut5 #S0\").click(function(){acd5_state(0);});$(\"#acdaut5 #S1\").click(function(){acd5_state(1);});$(\"#acdaut5 #S2\").click(function(){acd5_state(2);});$(\"#acdaut5 #S3\").click(function(){acd5_state(3);});$(\"#acd5 #N0\").click(function(){acd5_node(0, 1);});$(\"#acd5 #N1\").click(function(){acd5_node(1, 0);});$(\"#acd5 #N2\").click(function(){acd5_node(2, 0);});</script>"
       ],
       "text/plain": [
-       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f0c480ea1b0> >"
+       "<spot.acd; proxy of <Swig Object of type 'spot::acd *' at 0x7f147010d630> >"
       ]
      },
-     "execution_count": 58,
+     "execution_count": 60,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -9984,7 +10215,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 59,
+   "execution_count": 61,
    "id": "94a02201",
    "metadata": {},
    "outputs": [
@@ -10091,10 +10322,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480e2300> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f147010d5a0> >"
       ]
      },
-     "execution_count": 59,
+     "execution_count": 61,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -10105,7 +10336,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 60,
+   "execution_count": 62,
    "id": "d484ba8f",
    "metadata": {},
    "outputs": [
@@ -10118,11 +10349,11 @@
        "<!-- Generated by graphviz version 2.43.0 (0)\n",
        " -->\n",
        "<!-- Pages: 1 -->\n",
-       "<svg width=\"494pt\" height=\"181pt\"\n",
-       " viewBox=\"0.00 0.00 494.00 181.44\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n",
-       "<g id=\"graph0\" class=\"graph\" transform=\"scale(1.0 1.0) rotate(0) translate(4 177.44)\">\n",
-       "<polygon fill=\"white\" stroke=\"transparent\" points=\"-4,4 -4,-177.44 490,-177.44 490,4 -4,4\"/>\n",
-       "<text text-anchor=\"start\" x=\"221.5\" y=\"-143.24\" font-family=\"Lato\" font-size=\"14.00\">[Büchi]</text>\n",
+       "<svg width=\"494pt\" height=\"165pt\"\n",
+       " viewBox=\"0.00 0.00 494.00 164.64\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n",
+       "<g id=\"graph0\" class=\"graph\" transform=\"scale(1.0 1.0) rotate(0) translate(4 160.64)\">\n",
+       "<polygon fill=\"white\" stroke=\"transparent\" points=\"-4,4 -4,-160.64 490,-160.64 490,4 -4,4\"/>\n",
+       "<text text-anchor=\"start\" x=\"221.5\" y=\"-141.44\" font-family=\"Lato\" font-size=\"14.00\">[Büchi]</text>\n",
        "<!-- I -->\n",
        "<!-- 0 -->\n",
        "<g id=\"node2\" class=\"node\">\n",
@@ -10221,10 +10452,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480f0420> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f147010d6f0> >"
       ]
      },
-     "execution_count": 60,
+     "execution_count": 62,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -10235,7 +10466,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 61,
+   "execution_count": 63,
    "id": "3332e850",
    "metadata": {},
    "outputs": [
@@ -10501,10 +10732,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480f0840> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1470116270> >"
       ]
      },
-     "execution_count": 61,
+     "execution_count": 63,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -10525,7 +10756,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 62,
+   "execution_count": 64,
    "id": "german-vienna",
    "metadata": {},
    "outputs": [
@@ -10595,10 +10826,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480f30c0> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1470116630> >"
       ]
      },
-     "execution_count": 62,
+     "execution_count": 64,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -10622,7 +10853,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 63,
+   "execution_count": 65,
    "id": "chemical-primary",
    "metadata": {},
    "outputs": [
@@ -10632,7 +10863,7 @@
        "(spot.trival_maybe(), spot.trival(True))"
       ]
      },
-     "execution_count": 63,
+     "execution_count": 65,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -10643,7 +10874,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 64,
+   "execution_count": 66,
    "id": "hispanic-floor",
    "metadata": {},
    "outputs": [
@@ -10706,10 +10937,10 @@
        "</svg>\n"
       ],
       "text/plain": [
-       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f0c480f3210> >"
+       "<spot.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1470116450> >"
       ]
      },
-     "execution_count": 64,
+     "execution_count": 66,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -10720,7 +10951,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 65,
+   "execution_count": 67,
    "id": "central-london",
    "metadata": {},
    "outputs": [
@@ -10730,7 +10961,7 @@
        "(spot.trival(True), spot.trival(True))"
       ]
      },
-     "execution_count": 65,
+     "execution_count": 67,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -10750,7 +10981,7 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 3",
+   "display_name": "Python 3 (ipykernel)",
    "language": "python",
    "name": "python3"
   },
diff --git a/tests/python/zlktree.py b/tests/python/zlktree.py
index e1b0c9e7b..c3cb262f2 100644
--- a/tests/python/zlktree.py
+++ b/tests/python/zlktree.py
@@ -152,3 +152,12 @@ tc.assertTrue(a.equivalent_to(b))
 b = spot.acd_transform_sbacc(a, False)
 tc.assertEqual(str(b.acc()), '(2, Fin(0) & Inf(1))')
 tc.assertTrue(a.equivalent_to(b))
+
+
+# This used to be very slow.
+c = spot.acc_cond("Rabin 9")
+n = spot.zielonka_tree(c).num_branches()
+tc.assertEqual(n, 362880)
+opt = spot.zielonka_tree_options_MERGE_SUBTREES;
+n = spot.zielonka_tree(c, opt).num_branches()
+tc.assertEqual(n, 9)