1. The Origin of Analytic Geometry
2. J. L. Coolidge, A History of Geometrical Methods, Oxford, 1940, p. 126.
3. The Geometry of René Descartes (translated by David Eugene Smith and Marcia L. Latham), New York, Dover reprint, 1954, pp. 334–335.
4. Oeuvres de Descartes (edited by Charles Adam and Paul Tannery, 12 vols, and supplement), Paris, 1897-1913, vol. VI, pp. 17–18.