Wed, 01 Aug 2012 00:00:00 GMT

Seven circle theorem, an applet illustrating the fact that if six circles are tangent to and completely surrounding a seventh circle, then connecting opposite points of tangency in pairs forms three lines that meet in a single point, by Michael Borcherds. Other applets by Borcherds include Poncelet's porism, a similar porism with an ellipse and a parabola and with two ellipses, and more generally with two conics of variable type.