In the first two moves the wK and the front piece of the black battery move into position. The route of the black piece is determined by the need to unguard d6/e3 for the wK. The wSg5 then self-blocks the square vacated by the wK, then Black sets up a battery by moving the rear piece into position. A white check then forces a black double-check mate.

In both mates the bB is on c5 and the bR on d3, with the mating move being made from d4! Their routes are Bf8-g7-d4-c5 and Bf8-c5; and Rh3-d3 and Rh3-h4-d4-d3, making a kind of Rundlauf. The wR and wB exchange roles in making the white check (with self-block) or else guarding b3. The bS guards e5 or f4 in the mates. A fine problem!