As a side note Dijkstra has a wonderful generalization and it has a nice proof at https://www.cut-the-knot.org/pythagoras/Stevens.shtml https://www.cut-the-knot

As a side note Dijkstra has a wonderful generalization and it has a nice proof at https://www.cut-the-knot.org/pythagoras/Stevens.shtml https://www.cut-the-knot.org/pythagoras/Stevens.shtml and I was wondering whether this is old as well.