TIL that Debian folks do not consider CC-BY to be Free: v1: https://lists.debian.org/debian-legal/2004/04/msg00031.html v2: https://web.archive.org/web/20140202132111/http://evan.prodromou.name/ccsummary/ccsummary.html v3: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=431794