In Henri Picciotto's [url=https://www.mathedpage.org/geometry-labs/]Geometry Labs[/url] book, he proposes this problem: which quadrilaterals can be made with two copies of the same triangle. ([url=https://www.mathedpage.org/geometry-labs/gl/gl-6.pdf]Section 6.4[/url])[br][br]The green and purple are copies of the blue, and you can click on a copy to flip it.