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Josefsson, Martin: Characterizations of Bicentric Quadrilaterals. Forum Geometricorum, 2010, nro 10, s. 165–173. ISSN 1534-1178. Artikkelin verkkoversio (pdf). Viitattu 28.9.2013. (englanniksi)
Radić, Mirko & Kaliman, Zoran & Kadum, Vladimir: A condition that a tangential quadrilateral is also a chordal one. Mathematical Communications, 2007, nro 12, s. 33–52. Osijek, Kroatia: University of Osijek. ISSN 1331-0623. Artikkelin verkkoversio (pdf). Viitattu 28.9.2013. (englanniksi)