No.1697 (TM)

Breton-specific mates, with 3.Kxa6[-c6]?? being self-check from wRg6, and 3.Kxb8[-c7]?? being self-check from wBf4. In order for this to work a black B or R must be removed, but White has no spare moves. Therefore Black must use his two moves to capture a white B/R, after which a black B/R will also disappear. It’s also interesting that Black must choose the capturing piece carefully, because the wrong capturing piece will close a line needed on White’s first move.
Four pairs of pieces exchange functions. The white Rg3/Bc1 either guard the mating unit (in an X-ray guard!) or else are captured. The white Rg8/Bd3 either give mate or else guard squares next to the black K. The black Re5/Bf6 either capture a white unit or else disappear when a white unit is captured. The black Rc7/Bc6 are either used in the X-ray guard or else block a square next to the black K.