This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Completequads.svg complete quadrangle left and complete quadrilateral right en David Eppstein en David Eppstein original upload log page en Completequads David Eppstein bytes no complete quadrangle left and complete quadrilateral right Projective geometry Lines and points Files by User David Eppstein from en Duality mathematics