Pappus' proof, relying solely on Euclidean geometry, ran over many pages. The modern proof is much simpler and uses the powerful method of circle inversion, invented in the 1820's by Jacob Steiner. Try manipulating the figure by clicking and dragging one of the orange points, A, or B. Note that as you do this, not only do you re-size the arbelos and the chain of inscribed circles, you also cause the corresponding black point, A' or B', to move as well. Point A' is the inverse of point A, and point B' is the inverse of point B, both points having been inverted through a circle whose center is at point C.