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+Finding all the elementary circuits of a directed graph
+-------------------------------------------------------
+
+Algorithm by R. Tarjan
+
+
+    Enumeration of the elementary circuits of a directed graph
+    R. Tarjan, SIAM Journal on Computing, 2 (1973), pp. 211-216
+    http://dx.doi.org/10.1137/0202017
+
+Usage
+-----
+
+    python cycles.py 4 0,1 0,2 1,0 1,3 2,0 3,0 3,1 3,2
+
+First argument is the number of vertices. Subsequent arguments are ordered
+pairs of comma separated vertices that make up the directed edges of the
+graph.
+
+DOT file input
+--------------
+
+For simplicity, there is no DOT file parser included but the following allows
+to create a suitable argument string for simple DOT graphs.
+
+Given a DOT file of a simple (no labels, colors, styles, only pairs of
+vertices...) directed graph, the following line produces commandline
+arguments in the above format for that graph.
+
+	echo `sed -n -e '/^\s*[0-9]\+;$/p' graph.dot | wc -l` `sed -n -e 's/^\s*\([0-9]\) -> \([0-9]\);$/\1,\2/p' graph.dot`
+
+The above line works on DOT files like the following:
+
+    digraph G {
+      0;
+      1;
+      2;
+      0 -> 1;
+      0 -> 2;
+      1 -> 0;
+      2 -> 0;
+      2 -> 1;
+      }
+
+It would produce the following output:
+
+    3 0,1 0,2 1,0 2,0 2,1