“Poncelet discovered a beautiful theorem that if you have a {{w|triangle}}... whose vertices are on one ellipse, and whose sides touch another ellipse, then... if there is one solution, there are infinitely many solutions. ...This ...beautiful theorem ...used to be taught ...in schools where they taught geometry. ...[T]he two ellipses, you may think, look very different from two circles, but by elementary {{w|projective geometry}} you can always move them so that ...they're both circles.”