http://repository.uhamka.ac.id/id/eprint/11992/
Peer Reviu_Is exemplification the one and only way to describe that empty set is subset
of any sets?
Samsul Maarif, SMF
http://repository.uhamka.ac.id/id/eprint/11992/1/Jurnal%20Inter_Is%20Examplification%20The%20one%20and%20only%20Way.pdf