Dear Geoff, Many congratulations on your proof...
When I set the puzzle, I thought three things: 1. I am really setting this for Geoff to solve. 2. He will certainly solve it and will probably be the first to publish. 3. His proof will either match mine or be more elegant. I was right on all three counts. Your proof is just what I had in mind. Once you spot those two triangles it is obvious that they are similar and the rest comes out in the wash! Very best wishes Frank --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial