"salonowiec" <email@example.com> wrote in message news:firstname.lastname@example.org... >Years ago I was busy with solving "Soddy Circles" - circles tangent to three given ones. I used some kind of operation that transformed: circle to circle or circle to a straight line or straight line to circle etc. Can anybody remind what this transformation was? Thank you...
Perhaps Mobius transformations of the complex plane?
These are maps from C to C of the form:
z --> (az + b) / (cz + d)
for complex constants a,b,c,d, where ad != bc. They all map lines and circles to lines and circles.