--- a/progs/catastrophic.py	Sun Sep 23 09:04:24 2018 +0100
+++ b/progs/catastrophic.py	Mon Sep 24 11:05:39 2018 +0100
@@ -2,15 +2,26 @@
 import re
 import sys
 
-# case of catastrophic backtracking in Python
+# A case of catastrophic backtracking in Python
 #
 # regex: (a?){n} a{n}
 # strings: aa...
 #
+# call with:
+#
+#   > ./catastrophic.py 20
+#
+# or
+#
+#   > ./catastrophic.py 28
+#
+#
 # call with timing as:
 #
 #   > time ./catastrophic.py 20
 
+
+
 # counter n given on the command line
 cn = sys.argv[1]