Given an arbitrary Quadrilateral, place a Square outwardly on each side, and connect the centers of opposite Squares. Then the two lines are of equal length and cross at a Right Angle.

**References**

Kitchen, E. ``Dörrie Tiles and Related Miniatures.'' *Math. Mag.* **67**, 128-130, 1994.

© 1996-9

1999-05-26