The Org Mode section on including files: https://orgmode.org/manual/Include-files.html
seems to be missing a detail. It appears that relative paths are allowed, I assume they would be relative to the directory of the parent file. That is to say if I have file "monday.org" including file "sunday.org", and they are in the same folder, then I could use this syntax: #+INCLUDE: "sunday.org" Is that correct?