Thales' Theorem

box -1, -1, 7, 4 vertical a(#A, -2, 10, 170) = 170 c = circle(point(3, 0), 3) P = point(c, a°) M = point(0, 0) N = point(6, 0) draw (M.N.P) c 0° 180° gray end label M, P, N right, 0.6

This interactive script can be converted into an animated GIF using :

$> eukleides -a A81 thales.euk -o thales.ps

to create a multi-page PS document, and then (provided ImageMagik is installed) :

$> convert -delay 5 thales.ps thales.gif