Self-intersecting polygons, crossed polygons, or self-crossing polygons are polygons some of whose edges cross each other. They contrast with simple polygons, whose edges never cross. Some types of self-intersecting polygons are: * the crossed quadrilateral, with four edges * the antiparallelogram, a crossed quadrilateral with alternate edges of equal length * the crossed rectangle, an antiparallelogram whose edges are two opposite sides and the two diagonals of a rectangle, hence having two edges parallel * Star polygons * pentagram, with five edges * heptagram, with seven edges * octagram, with eight edges * enneagram or nonagram, with nine edges * decagram, with ten edges * hendecagram, with eleven edges * dodecagram, with twelve edges (en)