--- tahoe-lafs-1.5.0.orig/debian/copyright
+++ tahoe-lafs-1.5.0/debian/copyright
@@ -229,3 +229,9 @@
 project, including the file 'statistics.py', under both the GNU General Public
 License, version 2 or later, and under the Transitive Grace Period Public
 License, version 1 or later."
+
+The original author of file src/allmydata/util/mathutil.py , Zooko
+Wilcox-O'Hearn, granted full rights to allmydata.com to re-license it as
+they see fit, and they reclicensed it the same terms as Tahoe-LAFS
+itself: you may use it under GPL version 2 or greater at your option or
+under TGPPL version 1 or greater at your option.