Support für Coalition Chess

[thomas-maeder]

Probably without knowing fairy chess, the famous (music) composer Arnold Schönberg invented a fairy chess variant that he called Coalition Chess (Bündnisschach or Koalitionsschach).

Cf. https://www.schoenberg.at/index.php/de/schoenberg/as-kennenlernen/koalitionsschach

Now Popeye currently only supports 8x8 boards (or smaller, if one uses holes), but not 10x10.

But at least the added fairy pieces Flyer (Flieger), Submarine (Unterseeboot) and Machine Gun (Maschinengewehr) could be easily supported by Popeye.