[color=#000000]What (not-too-often-seen) geometry theorem is dynamically being illustrated in the applet below?[br](Feel free to move the white vertices and/or adjust the sliders at any time!) [/color]
[color=#000000][b]Finsler-Hadwiger Theorem: [/b][/color][br][br][color=#000000]"Suppose that ABCD and AB'C'D' are two squares with common vertex A. Let E and G be the midpoints of B'D and D'B respectively, and let F and H be the centers of the two squares. If this is the case, then quadrilateral EFGH will always be a square as well"! (This description taken right from [url=https://en.wikipedia.org/wiki/Finsler%E2%80%93Hadwiger_theorem]Wikipedia's description[/url].) [/color]