Now the thematic captured unit can only be R, since a2 is a light square. Black's prior move cannot have been with K, since it would result in impossible double check. So Sb1 just came from d2. Sd2 did not interfere with the Staugaard castling, as only the rook passed over e4.
Now the thematic captured unit can only be R, since a2 is a light square. Black's prior move cannot have been with K, since it would result in impossible double check. So Sb1 just came from d2. Sd2 did not interfere with the Staugaard castling, as only the rook passed over e4.
