For explanations about the Desargues polar of a point P w.r.t to a triangle, watch the Youtube video :[br][list][*][url=https://youtu.be/PbA4Js3qKOQ]Orthocenters exist! | Universal Hyperbolic Geometry 10 | NJ Wildberger[/url][/*][/list][list][*]pg 9: @32:28 Desargues theorem (a foundational theorem of projective geometry)[br][/*][/list]