Babson Task

The Babson task is a kind of chess problem of the form "white to move and mate black in N moves against any defence" with the following play:

1. White makes his first move.
2. Black defends by promoting a pawn to queen, rook, bishop or knight.
3. White responds by promoting a pawn to queen, rook, bishop or knight respectively (if black promoted to rook, so does white, if black promoted to knight, so does white and so on). No other promotion (or any other move) leads to mate in the stipulated number of moves.

The task is named after the first person to speculate about the possibility of such a problem, Joseph Ney Babson. It is regarded as one of the greatest challenges for a composer of chess problems to devise a satisfying Babson task problem, and for around half a century the task was considered to be near-impossible in directmate form.

Technically, the task can be regarded as a form of Allumwandlung with corresponding promotions by black and white (an Allumwandlung is a problem which contains, at some point in the solution, promotions to each of the four possible pieces — such problems had already been composed before Babson devised his task).