1. M. Hazewinkel (ed.), Encyclopaedia of Mathematics (Kluwer, Alphen aan den Rijn, 1994), http://www.encyclopediaofmath.org
2. A.A. Savelov, Planar Curves (Moscow, 1960) (In Russian)
3. J.D. Lawrence, A Catalog of Special Plane Curves. Dover Books on Mathematics (Courier Dover, Mineola, 2013), p. 186
4. A. Schioner, Albrecht Dürer: Genie zwischen Mittelalter und Neuzeit (Pustet, Regensburg, 2011)
5. A. Dürer, Instructions for Measuring with Compass and Ruler (Nuremberg, 1525)