Bogomolny, Alexander, "Inscriptible and Exscriptible Quadrilaterals", Interactive Mathematics Miscellany and Puzzles, [1]. Accessed 2011-08-18.
fau.edu
forumgeom.fau.edu
Josefsson, Martin, Similar Metric Characterizations of Tangential and Extangential Quadrilaterals, Forum Geometricorum Volume 12 (2012) pp. 63-77 [2]Archived 2022-01-16 at the Wayback Machine
Hajja, Mowaffaq, A Very Short and Simple Proof of “The Most Elementary Theorem” of Euclidean Geometry, Forum Geometricorum Volume 6 (2006) pp. 167–169 [3]Archived 2021-11-19 at the Wayback Machine
Josefsson, Martin, Similar Metric Characterizations of Tangential and Extangential Quadrilaterals, Forum Geometricorum Volume 12 (2012) pp. 63-77 [2]Archived 2022-01-16 at the Wayback Machine
Hajja, Mowaffaq, A Very Short and Simple Proof of “The Most Elementary Theorem” of Euclidean Geometry, Forum Geometricorum Volume 6 (2006) pp. 167–169 [3]Archived 2021-11-19 at the Wayback Machine