More on the rule history and this puzzle. https://en.wikipedia.org/wiki/Promotion_%28chess%29#1862_British_Chess_Association_rule https://en.wikipedia.org/wiki

More on the rule history and this puzzle. https://en.wikipedia.org/wiki/Promotion_%28chess%29#1862_British_Chess_Association_rule https://en.wikipedia.org/wiki/Promotion_%28chess%29#1862_Bri... "The broad language of Law XIII also appears to allow promotion to any piece of either color. This led to the whimsical endgame study diagrammed at right. White is to play and checkmate in one move."