Posamentier et al. 2013, p.71. Posamentier, Alfred S.; Farber, William; Germain-Williams, Terri L.; Paris, Elaine; Thaller, Bernd; Lehmann, Ingmar (2013). 100 Commonly Asked Questions in Math Class. Corwin Press. ISBN978-1-4522-4308-5.
Medina et al. 2004, p.617. Medina, Jesús; Ojeda-Aciego, Manuel; Valverde, Agustín; Vojtáš, Peter (2004). "Towards Biresiduated Multi-adjoint Logic Programming". In Conejo, Ricardo; Urretavizcaya, Maite; Pérez-de-la-Cruz, José-Luis (eds.). Current Topics in Artificial Intelligence: 10th Conference of the Spanish Association for Artificial Intelligence, CAEPIA 2003, and 5th Conference on Technology Transfer, TTIA 2003, November 12-14, 2003. Lecture Notes in Computer Science. Vol.3040. San Sebastian, Spain: Springer. doi:10.1007/b98369. ISBN978-3-540-22218-7.
Barbeau 1968, p.183. See Book VII, Proposition 5, in David E. Joyce's online edition of Euclid's Elements Barbeau, Alice Mae (1968). A Historical Approach to the Theory of Groups. Vol.2. University of Wisconsin--Madison.
Medina et al. 2004, p.617. Medina, Jesús; Ojeda-Aciego, Manuel; Valverde, Agustín; Vojtáš, Peter (2004). "Towards Biresiduated Multi-adjoint Logic Programming". In Conejo, Ricardo; Urretavizcaya, Maite; Pérez-de-la-Cruz, José-Luis (eds.). Current Topics in Artificial Intelligence: 10th Conference of the Spanish Association for Artificial Intelligence, CAEPIA 2003, and 5th Conference on Technology Transfer, TTIA 2003, November 12-14, 2003. Lecture Notes in Computer Science. Vol.3040. San Sebastian, Spain: Springer. doi:10.1007/b98369. ISBN978-3-540-22218-7.