Interactive step by step proof of the van Aubel's theorem. Instructions: Use the buttons: Next, Previous, First, Last and Go to any step.
Given an arbitrary planar quadrilateral UTAH, place a square outwardly on each side, and connect the centers of opposite squares: M, O, N, and Y. Then van Aubel's theorem states that the two lines MO and NY are of equal length and cross at a right angle. 

