Applet, stereo version

This applet deals comprehensively with hexlet.

This applet uses Javaview

In this applet, there is great flexibility to choose radii, transparencies, etc., which allows you to clearly see the effect of the transformation used in the proof - an inversion centered at the tangency point of the blue and red surfaces - to reduce the question to a simpler one, with two planes instead of two spheres: