I believe that the solution to Problem M/A1 in the recent July/August issue of *MIT News *has a subtle but significant error. In particular, in the given explanation of why the White king cannot have moved last, the claim "there is no previous Black move that could have put the White king into check" is incorrect. A Black bishop could have been on b8 and moved to c7, discovering a check from the Black queen, and then the White king could have captured that bishop on c7. Indeed, to show that this is possible, place the White king on c8, a White knight on a6, a Black knight on c7, and a Black bishop on b8 (leave all other pieces as-is), with White to move: Then a sequence of moves leading to the given position is: Nxc7+ Bxc7+ Kxc7 which would mean that it is now Black's move...if the position were legal. Nonetheless, I do believe the position is impossible. To prove, we consider which piece could have most recently moved: the Black king or the White rook. It could not have been the White rook, because its only move would have been from f8, where it would have been checking the Black king. So the Black king must have moved more recently than the White rook, and it must have moved from d8 to e8. But when the Black king made this move, the White king must have been at a8 or b8, since it has no way of getting to squares a8, b8, c8, or c7 without passing through e8. In particular, the Black queen cannot have already been at a8. And once the Black king moved to e8 and stayed there, there is no way for the Black queen to get to a8, as the White king is now confined to a8, b8, c8, and c7, so regardless of whether the Black queen moved to a8 from b8, c8, or d8, it would have been checking the White king before its move, which of course is illegal. Best regards, --David Patrick