Hey, on the Sail machine, user names were 3 letters, and you only got one level of subdirectory, also 3 letters long. So, in the syntax of the time, “[ACP,DEK]” was it!

(Six bits for each upper-case alphanumeric character means a 6-character directory name neatly fits into a 36-bit word on the DEC PDP-10. And file names were limited to 6 characters for the same reason; extensions were 3 characters, with the remaining 18 bits for file meta-data, I think.)