The Babson task is a kind of chess problem (composition chess) of the form "white to move and mate black in N moves against any defence" with the following play:
White makes his first move.
Black defends by promoting a pawn to queen, rook, bishop or knight.
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 possibilty 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).
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This 1912 problem by Wolfgang Pauly is, as it were, a three-quarter Babson task - three of black's promotions are matched by white. White to move and mate in four:
The key is b3 (see algebraic notation for an explanation of the notation used), after which there are the following lines:
1... a1Q 2. f8Q Qb2 3. Qa8 Qxc1 4. Qf3 mate
1... a1R 2. f8R a2 3. Rf6 Kxh4 4. Rh6 mate
1... a1N 2. f8N a2 3. Ng6 Nxb3 4. Nf4 mate
However, this is not a full Babson, because 1... a1B 2. f8B does not work - white must instead play 2. f8Q, with similar play to above.
The earliest Babson tasks are all in the form of a selfmate - this is where white, moving first, must force black to mate him against his will within a specified number of moves. In 1914, Babson himself published a selfmate which achieved the task, although three different white pawns shared the promotions. The first problem in which a single black and single white pawn were involved in the promotions was by Henry William Bettmann, and won 1st prize in the Babson Task Tourney 1925-26.
The key move in Bettmann's problem (left) is 1.a8=B, after which the play goes:
1...fxg1=Q 2. f8=Q
2... Qxf1/Qxc5 3.b5 Qxb5#
2... Q-any 3.AnyxQ Rxa6#
1...fxg1=R 2. f8=R R-any 3.anyxR Rxa6#
1...fxg1=B 2. f8=B B-any 3.anyxB Rxa6#
1... fxg1=N 2. f8=N S-any 3.anyxN Rxa6#
A number of other selfmate Babson tasks with one pawn of each colour doing all the promotions followed this one.
Composing a Babson task problem in directmate form (where white moves first, and must checkmate black against any defence within a stipulated number of moves) was thought so difficult that very little effort was put into solving it until the 1960s, when Pierre Drumare began his work on the problem which would occupy him for the next twenty years or so. He managed to compose a Babson task problem using nightriders (a fairy piece which moves like a knight, but can make any number of knight-like moves in the same direction in one go) instead of knights, but found it hard to devise one using normal pieces - because of their limited range, it is difficult to justify white promoting to a knight because of black promoting to one way over the other side of the board.
When Drumare did eventually succeed using conventional pieces in 1980, the result was regarded as highly unsatisfactory, even by Drumare himself. It is a mate in five (first published Memorial Seneca, 1980):
The key is Rf2, after which black captures on b1 are answered by white captures on g8.
Efficiency in chess problems is considered a great boon, but Drumare's attempt is very inefficient - no less than 31 men are on the board. It also has six promoted pieces in the initial position (even a single promoted piece is considered something of a "cheat" in chess problems), which is in any case illegal - it could not be reached in the course of a game. Despite all these flaws, it is the first complete Babson task.
In 1982, two years after composing this problem, Drumare gave up, saying that the Babson task would never be satisfactorily solved.
The following year, Leonid Yarosh, a football coach from Kazan then virtually unknown as a problem composer, came up with a much better Babson task problem than Drumare's - the position is legal, it is much simpler than Drumare's problem, and there are no promoted pieces on board. First published in March 1983 in the famous Russian chess magazine Shakhmaty v SSSR, this is generally thought of as the first satisfactory solution of the Babson task. Drumare himself had high praise for the problem. It is a mate in four:
The key is 1.Rxh4, and the main lines are:
cxb1Q 2.axb8Q Qxb2 (2... Qe4 3.Qxf4 Qxf4 4.Rxf4 mate) 3.Qb3 Qc3 4.Qxc3#
cxb1R 2.axb8R Rxb2 3.Rb3 Kxc4 4.Rxf4 mate
cxb1B 2.axb8B Be4 3.Bxf4 Bxh1 4.Be3 mate
cxb1N 2.axb8N Nxd2 3.Nc6+ Kc3 4.Rc1 mate
However, Yarosh's problem has a small flaw - the key is a capture, something which is generally frowned upon in problems. Yarosh worked on the problem, and in August 1983 an improved version of it with a non-capturing key appeared in Shakhmaty v SSSR. It is generally considered one of the greatest chess problems ever composed. Again, mate in four:
The key here is non-capturing and also thematic (it is logically related to the rest of the solution): 1.a7. The variations are largely the same as in the original:
axb1Q 2.axb8Q Qxb2 (2... Qe4 3.Qxf4 Qxf4 4.Rxf4 mate) 3.Qxb3 Qc3 4.Qbxc3 mate
axb1R 2.axb8R Rxb2 3.Rxb3 Kxc4 4.Qa4 mate
axb1B 2.axb8B Be4 3.Bxf4 Bxa8 4.Be3 mate
axb1N 2.axb8N Nxd2 3.Qc1 Ne4 4.Nc6 mate
Yarosh composed a completely different Babson task problem in 1983 and another in 1986. Several other Babsons have since been composed by other authors.
In the August 2003 issue of the German problem magazine Die Schwalbe, the problem to the right, a mate in four by Peter Hoffmann appeared. Hoffmann had previously published a number of conventional directmate Babsons, but this one is significant as it is the first cyclic Babson: rather than black promotions being matched by white, they are related in cyclic form: black promoting to a queen means white must promote to a bishop, black promoting to a bishop means white must promote to a rook, black promoting to a rook means white must promote to a knight, and black promoting to a knight means white must promote to a queen.
The key is 1.Nxe6, threatening 2.hxg8Q and 3.Qf7#. The thematic defences are:
1...d1Q 2.hxg8B (2.hxg8Q? Qd7+ 3.Bxd7 is stalemate), threatening 3.c4+ Qmoves 4.BxQ#
2...Qd7+ 3.Bxd7 Kxg6 4.Rxh6#
2...Qxc1 3.Rxg5 (threat: 4.Rf5#) hxg5 4.Qh8#
1...d1R 2.hxg8N (2.hxg8Q? Rd4+ 3. c4 stalemate) Kxe6 3.Qxe2+ K-moves 4.Qe5#
1...d1B 2.hxg8R (2.hxg8Q? stalemate) Kxe6 3.Rd8 3.Kf6 Rd6#
1...d1N 2.hxg8Q Nxb2+ 3.moves and 4.Qf7#
There are also a number of sidelines.
As with Drumare's original Babson task, the problem uses promoted pieces and has a capturing key, but it is nontheless remarkable for being the first published cyclic Babson.
Jeremy Morse, Chess Problems Tasks and Records (Faber and Faber, 1995, revised edition 2001) - contains a chapter on the Babson task