"The use of ARPA as a Top Level Domain was only temporary, until its hosts selected some other domain. " Someone tell that to in-addr.arpa, lol. It's certainly

"The use of ARPA as a Top Level Domain was only temporary, until its hosts selected some other domain. " Someone tell that to in-addr.arpa, lol. It's certainly still around https://www.iana.org/domains/arpa https://www.iana.org/domains/arpa The author really should've checked later RFCs.