Editing Quadrilateral (section)

==Complex quadrilaterals ==
[[File:DU21 facets.png|thumb|upright=0.8|An antiparallelogram]]
A [[list of self-intersecting polygons|self-intersecting]] quadrilateral is called variously a '''cross-quadrilateral''', '''crossed quadrilateral''', '''[[butterfly]] quadrilateral''' or '''[[bow-tie]] quadrilateral'''. In a crossed quadrilateral, the four "interior" angles on either side of the crossing (two [[acute angle|acute]] and two [[reflex angle|reflex]], all on the left or all on the right as the figure is traced out) add up to 720°.<ref>{{cite web|url=http://mysite.mweb.co.za/residents/profmd/stars.pdf|title=Stars: A Second Look|website=Mysite.mweb.co.za|access-date=March 1, 2022|archive-date=March 3, 2016|archive-url=https://web.archive.org/web/20160303182521/http://mysite.mweb.co.za/residents/profmd/stars.pdf|url-status=dead}}</ref>

*[[Isosceles trapezoid#Self-intersections|Crossed trapezoid]] (US) or trapezium (Commonwealth):<ref>{{cite web | url=https://blogs.adelaide.edu.au/maths-learning/2016/04/06/the-crossed-trapezium/ | title=The crossed trapezium | last=Butler | first=David | date=2016-04-06 | website=Making Your Own Sense | access-date=2017-09-13}}</ref> a crossed quadrilateral in which one pair of nonadjacent sides is parallel (like a [[trapezoid]]).
*[[Antiparallelogram]]: a crossed quadrilateral in which each pair of nonadjacent sides have equal lengths (like a [[parallelogram]]).
*[[Crossed rectangle]]: an antiparallelogram whose sides are two opposite sides and the two diagonals of a [[rectangle]], hence having one pair of parallel opposite sides.
*[[Square#Crossed square|Crossed square]]: a special case of a crossed rectangle where two of the sides intersect at right angles.