Package: www.debian.org Followup-For: Bug #763005 This problem still exists on the website.
https://www.debian.org/releases/stable/installmanual leads to https://www.debian.org/releases/stable/amd64/ which says This document contains installation instructions for the Debian GNU/Linux 9 system (codename “stretch”), for the 64-bit PC (“amd64”) It is not clear at all if it's the wrong manual, or if it's just a wrong string. I don't know either, but I know it's very confusing.
