We prove the Ptolemaean inequality andPtolemaeus' theorem in the closure of complex hyperbolic planes endowed with theCygan metric.
PLATIS, IOANNIS D. and SÖNMEZ, NİLGÜN
"The Ptolemaean inequality in the closure of complex hyperbolic planes,"
Turkish Journal of Mathematics: Vol. 41:
5, Article 2.
Available at: https://journals.tubitak.gov.tr/math/vol41/iss5/2