MJ Ray mjr@phonecoop.coop writes:
"Copylefted software is free software whose distribution terms do not let redistributors add any additional restrictions when they redistribute or modify the software" but GPLv3 does let, through AGPLv3. http://www.gnu.org/philosophy/categories.html#CopyleftedSoftware
This looks like a mistake in categories.html. I'll mail FSF about this.