1 2 3 4 Josefsson, Martin (2014), "Properties of equidiagonal quadrilaterals", Forum Geometricorum, 14: 129–144. 1 2 Josefsson, Martin (2013), "Five Proofs of an Area Characterization of Rectangles" (PDF), Forum Geometricorum, 13: 17–21. ↑ Gerdes, Paulus (1988), "On culture, geometrical thinking and mathematics education", Educational Studies in Mathematics, 19 (2): 137–162, doi:10.1007/bf00751229, JSTOR 3482571. ↑ Josefsson, Martin (2012), "Characterizations of Orthodiagonal Quadrilaterals" (PDF), Forum Geometricorum, 12: 13–25. See in particular Theorem 7 on p.