diff --git a/NEWS b/NEWS
index 88cee43cf..7332d71fe 100644
--- a/NEWS
+++ b/NEWS
@@ -107,10 +107,12 @@ New in spot 1.99b (not yet released)
       sugar for [:*1..], and corresponds to the operator ⊕ introduced
       by Dax et al. (ATVA'09).
 
-    - GraphViz output now uses an horizontal layout by default.
-      The --dot option of the various command-line tools takes an
-      optional parameter to fine-tune the GraphViz output (including
-      vertical layout, round states, and named automata).
+    - GraphViz output now uses an horizontal layout by default.  The
+      --dot option of the various command-line tools takes an optional
+      parameter to fine-tune the GraphViz output (including vertical
+      layout, round states, and named automata).  The environment
+      variable SPOT_DOTEXTRA can also be used to add extra attributes
+      to the output graph.
 
     - Never claims can now be output in the style usd by Spin since
       version 6.2.4 (i.e., using do..od instead of if..fi, and with
diff --git a/src/bin/man/spot-x.x b/src/bin/man/spot-x.x
index aa30d6df3..b8d673040 100644
--- a/src/bin/man/spot-x.x
+++ b/src/bin/man/spot-x.x
@@ -11,6 +11,12 @@ spot-x \- Common fine-tuning options.
 
 [ENVIRONMENT VARIABLES]
 
+.TP
+\fBSPOT_DOTEXTRA\fR
+The contents of this variable is added to any dot output, immediately
+before the first state is output.  This makes it easy to override
+global attributes of the graph.
+
 .TP
 \fBSPOT_SATLOG\fR
 If set to a filename, the SAT-based minimization routines will append
diff --git a/src/taalgos/dotty.cc b/src/taalgos/dotty.cc
index 692eb9217..6ba8ba802 100644
--- a/src/taalgos/dotty.cc
+++ b/src/taalgos/dotty.cc
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2010, 2012, 2014 Laboratoire de Recherche et
+// Copyright (C) 2010, 2012, 2014, 2015 Laboratoire de Recherche et
 // Developpement de l Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -39,7 +39,11 @@ namespace spot
       void
       start()
       {
-        os_ << "digraph G {" << std::endl;
+        os_ << "digraph G {\n";
+
+	static const char* extra = getenv("SPOT_DOTEXTRA");
+	if (extra)
+	  os_ << "  " << extra << '\n';
 
         artificial_initial_state_ = t_automata_->get_artificial_initial_state();
 
diff --git a/src/tgbaalgos/dotty.cc b/src/tgbaalgos/dotty.cc
index c7c7793f9..702f4c726 100644
--- a/src/tgbaalgos/dotty.cc
+++ b/src/tgbaalgos/dotty.cc
@@ -30,6 +30,7 @@
 #include "tgba/tgbagraph.hh"
 #include "tgba/formula2bdd.hh"
 #include "tgbaalgos/sccinfo.hh"
+#include <cstdlib>
 
 namespace spot
 {
@@ -108,6 +109,12 @@ namespace spot
 	  }
 	if (opt_circles_)
 	  os_ << "  node [shape=\"circle\"]\n";
+	// Any extra text passed in the SPOT_DOTEXTRA environment
+	// variable should be output at the end of the "header", so
+	// that our setup can be overridden.
+	static const char* extra = getenv("SPOT_DOTEXTRA");
+	if (extra)
+	  os_ << "  " << extra << '\n';
 	os_ << "  I [label=\"\", style=invis, ";
 	os_ << (opt_horizontal_ ? "width" : "height");
 	os_ << "=0]\n  I -> " << aut_->get_init_state_number() << '\n';
diff --git a/src/tgbatest/readsave.test b/src/tgbatest/readsave.test
index 49fc0d20d..65e86c8bf 100755
--- a/src/tgbatest/readsave.test
+++ b/src/tgbatest/readsave.test
@@ -306,11 +306,14 @@ State: 3 "s3"
 [0] 1
 --END--
 EOF
-$autfilt -H input | $autfilt --dot=vcsn >output
+
+$autfilt -H input |
+    SPOT_DOTEXTRA='/* hello world */' $autfilt --dot=vcsn >output
 
 cat >expected <<EOF
 digraph G {
   node [shape="circle"]
+  /* hello world */
   I [label="", style=invis, height=0]
   I -> 3
   subgraph cluster_0 {
diff --git a/wrap/python/tests/automata.ipynb b/wrap/python/tests/automata.ipynb
index 1ed4ffc98..e7950ffe5 100644
--- a/wrap/python/tests/automata.ipynb
+++ b/wrap/python/tests/automata.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:6c1898261f2fab59f18fc3b6d75fe387d6f811b02935833fc74fa5e476796d4c"
+  "signature": "sha256:5d2a4f77c6bcffce3121cc011949d340222f35788edaf95171ae9917ea3794d6"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -12,7 +12,9 @@
      "cell_type": "code",
      "collapsed": false,
      "input": [
-      "import spot"
+      "import spot\n",
+      "import os\n",
+      "os.environ['SPOT_DOTEXTRA'] = 'node[style=filled,fillcolor=\"#88ddff\"]'"
      ],
      "language": "python",
      "metadata": {},
@@ -47,7 +49,7 @@
         "<!-- I -->\n",
         "<!-- 0 -->\n",
         "<g id=\"node2\" class=\"node\"><title>0</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"65\" cy=\"-69\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"65\" cy=\"-69\" rx=\"27\" ry=\"18\"/>\n",
         "<text text-anchor=\"middle\" x=\"65\" y=\"-65.3\" font-family=\"Times,serif\" font-size=\"14.00\">0</text>\n",
         "</g>\n",
         "<!-- I&#45;&gt;0 -->\n",
@@ -63,7 +65,7 @@
         "</g>\n",
         "<!-- 1 -->\n",
         "<g id=\"node3\" class=\"node\"><title>1</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"200\" cy=\"-109\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"200\" cy=\"-109\" rx=\"27\" ry=\"18\"/>\n",
         "<ellipse fill=\"none\" stroke=\"black\" cx=\"200\" cy=\"-109\" rx=\"31\" ry=\"22\"/>\n",
         "<text text-anchor=\"middle\" x=\"200\" y=\"-105.3\" font-family=\"Times,serif\" font-size=\"14.00\">1</text>\n",
         "</g>\n",
@@ -75,7 +77,7 @@
         "</g>\n",
         "<!-- 4 -->\n",
         "<g id=\"node4\" class=\"node\"><title>4</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"200\" cy=\"-18\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"200\" cy=\"-18\" rx=\"27\" ry=\"18\"/>\n",
         "<text text-anchor=\"middle\" x=\"200\" y=\"-14.3\" font-family=\"Times,serif\" font-size=\"14.00\">4</text>\n",
         "</g>\n",
         "<!-- 0&#45;&gt;4 -->\n",
@@ -92,7 +94,7 @@
         "</g>\n",
         "<!-- 2 -->\n",
         "<g id=\"node5\" class=\"node\"><title>2</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"453\" cy=\"-99\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"453\" cy=\"-99\" rx=\"27\" ry=\"18\"/>\n",
         "<text text-anchor=\"middle\" x=\"453\" y=\"-95.3\" font-family=\"Times,serif\" font-size=\"14.00\">2</text>\n",
         "</g>\n",
         "<!-- 1&#45;&gt;2 -->\n",
@@ -103,7 +105,7 @@
         "</g>\n",
         "<!-- 3 -->\n",
         "<g id=\"node6\" class=\"node\"><title>3</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"326\" cy=\"-99\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"326\" cy=\"-99\" rx=\"27\" ry=\"18\"/>\n",
         "<text text-anchor=\"middle\" x=\"326\" y=\"-95.3\" font-family=\"Times,serif\" font-size=\"14.00\">3</text>\n",
         "</g>\n",
         "<!-- 1&#45;&gt;3 -->\n",
@@ -152,7 +154,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7f79a4a46090> >"
+        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7fd82431b0f0> >"
        ]
       }
      ],
@@ -188,7 +190,7 @@
         "<!-- I -->\n",
         "<!-- 0 -->\n",
         "<g class=\"node\" id=\"node2\"><title>0</title>\n",
-        "<ellipse cx=\"56\" cy=\"-44\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"56\" cy=\"-44\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"56\" y=\"-40.3\">0</text>\n",
         "</g>\n",
         "<!-- I&#45;&gt;0 -->\n",
@@ -204,7 +206,7 @@
         "</g>\n",
         "<!-- 1 -->\n",
         "<g class=\"node\" id=\"node3\"><title>1</title>\n",
-        "<ellipse cx=\"173\" cy=\"-151\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"173\" cy=\"-151\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"173\" cy=\"-151\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"173\" y=\"-147.3\">1</text>\n",
         "</g>\n",
@@ -216,7 +218,7 @@
         "</g>\n",
         "<!-- 4 -->\n",
         "<g class=\"node\" id=\"node6\"><title>4</title>\n",
-        "<ellipse cx=\"173\" cy=\"-34\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"173\" cy=\"-34\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"173\" y=\"-30.3\">4</text>\n",
         "</g>\n",
         "<!-- 0&#45;&gt;4 -->\n",
@@ -233,7 +235,7 @@
         "</g>\n",
         "<!-- 3 -->\n",
         "<g class=\"node\" id=\"node4\"><title>3</title>\n",
-        "<ellipse cx=\"281.5\" cy=\"-178\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"281.5\" cy=\"-178\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"281.5\" y=\"-174.3\">3</text>\n",
         "</g>\n",
         "<!-- 1&#45;&gt;3 -->\n",
@@ -244,7 +246,7 @@
         "</g>\n",
         "<!-- 2 -->\n",
         "<g class=\"node\" id=\"node5\"><title>2</title>\n",
-        "<ellipse cx=\"391\" cy=\"-178\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"391\" cy=\"-178\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"391\" y=\"-174.3\">2</text>\n",
         "</g>\n",
         "<!-- 1&#45;&gt;2 -->\n",
@@ -293,7 +295,7 @@
         "</svg>"
        ],
        "text": [
-        "<IPython.core.display.SVG at 0x7f79a5729400>"
+        "<IPython.core.display.SVG at 0x7fd82694b470>"
        ]
       }
      ],
@@ -350,7 +352,7 @@
         "<!-- I -->\n",
         "<!-- 1 -->\n",
         "<g id=\"node2\" class=\"node\"><title>1</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"65\" cy=\"-22\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"65\" cy=\"-22\" rx=\"27\" ry=\"18\"/>\n",
         "<text text-anchor=\"middle\" x=\"65\" y=\"-18.3\" font-family=\"Times,serif\" font-size=\"14.00\">1</text>\n",
         "</g>\n",
         "<!-- I&#45;&gt;1 -->\n",
@@ -366,7 +368,7 @@
         "</g>\n",
         "<!-- 0 -->\n",
         "<g id=\"node3\" class=\"node\"><title>0</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"166\" cy=\"-22\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"166\" cy=\"-22\" rx=\"27\" ry=\"18\"/>\n",
         "<ellipse fill=\"none\" stroke=\"black\" cx=\"166\" cy=\"-22\" rx=\"31\" ry=\"22\"/>\n",
         "<text text-anchor=\"middle\" x=\"166\" y=\"-18.3\" font-family=\"Times,serif\" font-size=\"14.00\">0</text>\n",
         "</g>\n",
@@ -386,7 +388,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7f79a4aa1810> >"
+        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7fd8242f2870> >"
        ]
       }
      ],
@@ -420,7 +422,7 @@
         "<!-- I -->\n",
         "<!-- 1 -->\n",
         "<g id=\"node2\" class=\"node\"><title>1</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"65\" cy=\"-22\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"65\" cy=\"-22\" rx=\"27\" ry=\"18\"/>\n",
         "<text text-anchor=\"middle\" x=\"65\" y=\"-18.3\" font-family=\"Times,serif\" font-size=\"14.00\">1</text>\n",
         "</g>\n",
         "<!-- I&#45;&gt;1 -->\n",
@@ -436,7 +438,7 @@
         "</g>\n",
         "<!-- 0 -->\n",
         "<g id=\"node3\" class=\"node\"><title>0</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"166\" cy=\"-22\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"166\" cy=\"-22\" rx=\"27\" ry=\"18\"/>\n",
         "<ellipse fill=\"none\" stroke=\"black\" cx=\"166\" cy=\"-22\" rx=\"31\" ry=\"22\"/>\n",
         "<text text-anchor=\"middle\" x=\"166\" y=\"-18.3\" font-family=\"Times,serif\" font-size=\"14.00\">0</text>\n",
         "</g>\n",
@@ -456,7 +458,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7f79a4aa1930> >"
+        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7fd8242f2ab0> >"
        ]
       }
      ],
@@ -490,7 +492,7 @@
         "<!-- I -->\n",
         "<!-- 1 -->\n",
         "<g id=\"node2\" class=\"node\"><title>1</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"65\" cy=\"-18\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"65\" cy=\"-18\" rx=\"27\" ry=\"18\"/>\n",
         "<text text-anchor=\"middle\" x=\"65\" y=\"-14.3\" font-family=\"Times,serif\" font-size=\"14.00\">1</text>\n",
         "</g>\n",
         "<!-- I&#45;&gt;1 -->\n",
@@ -506,7 +508,7 @@
         "</g>\n",
         "<!-- 0 -->\n",
         "<g id=\"node3\" class=\"node\"><title>0</title>\n",
-        "<ellipse fill=\"none\" stroke=\"black\" cx=\"162\" cy=\"-18\" rx=\"27\" ry=\"18\"/>\n",
+        "<ellipse fill=\"#88ddff\" stroke=\"black\" cx=\"162\" cy=\"-18\" rx=\"27\" ry=\"18\"/>\n",
         "<text text-anchor=\"middle\" x=\"162\" y=\"-14.3\" font-family=\"Times,serif\" font-size=\"14.00\">0</text>\n",
         "</g>\n",
         "<!-- 1&#45;&gt;0 -->\n",
@@ -525,7 +527,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7f79a4aa18a0> >"
+        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7fd8242f2900> >"
        ]
       }
      ],
@@ -575,7 +577,7 @@
         "<!-- I -->\n",
         "<!-- 0 -->\n",
         "<g class=\"node\" id=\"node2\"><title>0</title>\n",
-        "<ellipse cx=\"109\" cy=\"-113\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"109\" cy=\"-113\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"109\" y=\"-109.3\">0</text>\n",
         "</g>\n",
         "<!-- I&#45;&gt;0 -->\n",
@@ -585,7 +587,7 @@
         "</g>\n",
         "<!-- 1 -->\n",
         "<g class=\"node\" id=\"node3\"><title>1</title>\n",
-        "<ellipse cx=\"22\" cy=\"-22\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"22\" cy=\"-22\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"22\" cy=\"-22\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"22\" y=\"-18.3\">1</text>\n",
         "</g>\n",
@@ -597,7 +599,7 @@
         "</g>\n",
         "<!-- 2 -->\n",
         "<g class=\"node\" id=\"node4\"><title>2</title>\n",
-        "<ellipse cx=\"109\" cy=\"-22\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"109\" cy=\"-22\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"109\" cy=\"-22\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"109\" y=\"-18.3\">2</text>\n",
         "</g>\n",
@@ -609,7 +611,7 @@
         "</g>\n",
         "<!-- 3 -->\n",
         "<g class=\"node\" id=\"node5\"><title>3</title>\n",
-        "<ellipse cx=\"196\" cy=\"-22\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"196\" cy=\"-22\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"196\" cy=\"-22\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"196\" y=\"-18.3\">3</text>\n",
         "</g>\n",
@@ -641,7 +643,7 @@
         "</svg>"
        ],
        "text": [
-        "<IPython.core.display.SVG at 0x7f798ea6e9b0>"
+        "<IPython.core.display.SVG at 0x7fd81c2fa898>"
        ]
       }
      ],
@@ -659,7 +661,7 @@
       {
        "metadata": {},
        "output_type": "pyout",
-       "prompt_number": 12,
+       "prompt_number": 10,
        "svg": [
         "<svg height=\"280pt\" viewBox=\"0.00 0.00 591.82 280.00\" width=\"592pt\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n",
         "<g class=\"graph\" id=\"graph0\" transform=\"scale(1 1) rotate(0) translate(4 276)\">\n",
@@ -668,7 +670,7 @@
         "<!-- I -->\n",
         "<!-- 6 -->\n",
         "<g class=\"node\" id=\"node2\"><title>6</title>\n",
-        "<ellipse cx=\"277.821\" cy=\"-212\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"277.821\" cy=\"-212\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"277.821\" cy=\"-212\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"277.821\" y=\"-208.3\">6</text>\n",
         "</g>\n",
@@ -685,7 +687,7 @@
         "</g>\n",
         "<!-- 0 -->\n",
         "<g class=\"node\" id=\"node3\"><title>0</title>\n",
-        "<ellipse cx=\"96.8206\" cy=\"-22\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"96.8206\" cy=\"-22\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"96.8206\" cy=\"-22\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"96.8206\" y=\"-18.3\">0</text>\n",
         "</g>\n",
@@ -697,7 +699,7 @@
         "</g>\n",
         "<!-- 1 -->\n",
         "<g class=\"node\" id=\"node4\"><title>1</title>\n",
-        "<ellipse cx=\"323.821\" cy=\"-22\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"323.821\" cy=\"-22\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"323.821\" cy=\"-22\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"323.821\" y=\"-18.3\">1</text>\n",
         "</g>\n",
@@ -709,7 +711,7 @@
         "</g>\n",
         "<!-- 2 -->\n",
         "<g class=\"node\" id=\"node5\"><title>2</title>\n",
-        "<ellipse cx=\"475.821\" cy=\"-22\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"475.821\" cy=\"-22\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"475.821\" cy=\"-22\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"475.821\" y=\"-18.3\">2</text>\n",
         "</g>\n",
@@ -721,7 +723,7 @@
         "</g>\n",
         "<!-- 3 -->\n",
         "<g class=\"node\" id=\"node6\"><title>3</title>\n",
-        "<ellipse cx=\"104.821\" cy=\"-117\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"104.821\" cy=\"-117\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"104.821\" cy=\"-117\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"104.821\" y=\"-113.3\">3</text>\n",
         "</g>\n",
@@ -733,7 +735,7 @@
         "</g>\n",
         "<!-- 4 -->\n",
         "<g class=\"node\" id=\"node7\"><title>4</title>\n",
-        "<ellipse cx=\"429.821\" cy=\"-117\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"429.821\" cy=\"-117\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"429.821\" cy=\"-117\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"429.821\" y=\"-113.3\">4</text>\n",
         "</g>\n",
@@ -745,7 +747,7 @@
         "</g>\n",
         "<!-- 5 -->\n",
         "<g class=\"node\" id=\"node8\"><title>5</title>\n",
-        "<ellipse cx=\"216.821\" cy=\"-117\" fill=\"none\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
+        "<ellipse cx=\"216.821\" cy=\"-117\" fill=\"#88ddff\" rx=\"18\" ry=\"18\" stroke=\"black\"/>\n",
         "<ellipse cx=\"216.821\" cy=\"-117\" fill=\"none\" rx=\"22\" ry=\"22\" stroke=\"black\"/>\n",
         "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"middle\" x=\"216.821\" y=\"-113.3\">5</text>\n",
         "</g>\n",
@@ -831,11 +833,19 @@
         "</svg>"
        ],
        "text": [
-        "<IPython.core.display.SVG at 0x7f798e982eb8>"
+        "<IPython.core.display.SVG at 0x7fd81c2fa7b8>"
        ]
       }
      ],
-     "prompt_number": 12
+     "prompt_number": 10
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [],
+     "language": "python",
+     "metadata": {},
+     "outputs": []
     }
    ],
    "metadata": {}