Back Cuadrángulo completo Spanish Quadrangle complet French Комплетен (целосен) четириаголник Macedonian Fullstendig firkant NB Quadrângulo completo Portuguese Полный четырёхугольник Russian Fullständig fyrhörning Swedish முழு நாற்கோணம் Tamil Повний чотирикутник Ukrainian 完全四边形 Chinese
In mathematics, specifically in incidence geometry and especially in projective geometry, a complete quadrangle is a system of geometric objects consisting of any four points in a plane, no three of which are on a common line, and of the six lines connecting the six pairs of points. Dually, a complete quadrilateral is a system of four lines, no three of which pass through the same point, and the six points of intersection of these lines. The complete quadrangle was called a tetrastigm by Lachlan (1893), and the complete quadrilateral was called a tetragram; those terms are occasionally still used.