applet by Tim Brzezinski showing Van Aubel's Theorem made using GeoGebra. Some generalizations of Van Aubel's theorem to similar quadrilaterals at Dynamic Geometry Sketches, interactive geometry sketches. QG-2P6: Outer and Inner Van Aubel Points by Chris Van Tienhoven at Encyclopedia of Quadri-Figures (EQF). Note concernant les centres de carrés construits sur les côtés d'un polygon quelconque by M. H. Van Aubel at HathiTrust Digital Library. Theorems about quadrilaterals