The Plachutta is a device in chess problems wherein the black side has either been lured or forced into accepting a sacrifice by the white side, thus entering two or more of its own similar moving pieces into mutual interference. Such problems will generally declare white is to move first and within how many moves white must declare checkmate. The first move made is called the key to the problem, as there is always one, and only one, correct key to each problem. The trick to chess problems of this type is that the key will generally be a sacrifice to create the Plachutta interference. The device is named after Joseph Plachutta.
Before examining a position illustrating this artificial Grimshaw, let us first inspect the situation by which a sacrifice could create interference on a chessboard. The limited range of the King and the Pawn, along with the non-linear movement of the Knight, limit interference with these pieces to coincidental affairs. In the world of chess problems, interference is generally a study of the movements of the Bishop, the Rook, and the Queen. Between these six pieces there are six different interactions. For similar linear movement we may consider two Rooks, a Rook and a Queen moving along the ranks and files, or a Bishop and a Queen moving along diagonals. For dissimilar linear movement we may consider a Bishop and a Rook, a Bishop and a Queen moving along the ranks and files, or a Rook and a Queen moving along diagonals. A Plachutta device is concerned only with the interactions of pieces owning similar linear movements. If there lies such a square on the board which may be reached by both pieces in any simililar linear movement pairing considered previously, that square would be a point of intersection between the two pieces. Should any enemy piece reach such an intersection, whose presence would otherwise lead to a checkmate, we may consider the sacrifice by white to be forced upon black. In the diagram immediately below, the square marked with an ¤ is the point of intersection between the similar moving Queen and Bishop from the first rank.
Here we see the true intent of Plachutta interference - the goal is often not the sacrifice itself, but the fact that after such sacrifice the piece which captures (in the diagram above, at square ¤), the capturing piece is now to be considered overloaded as it has but one move, and two squares it is now intended to defend. The diagrams below show a simple Plachutta example and a complicated one, respectively.
William Shinkman
White Rooks, 1910
White to play and mate in three.
This position shows black in death's throes. His King appears trapped on the eigth rank, and white is threatening checkmate by Rook on a8 and g8, if not for the defenses of the black Bishop and Queen, respectively. White would seek to break up the defense, and is able to with the key 1. d5, which draws the Queen and Bishop into Plachutta interference as without a capture, white has checkmate on either side of the King in two moves, which would not be an appropriate solution to a mate in three problem. The main line to the solution has only two branches.
- 1...Qxd5 2.Ra8+ Qxa8 3.Rg8#, the Queen interferes with the Bishop's defense of a8, which causes the Queen to abandon her defense of g8 to prevent 2.Ra8#
- 1...Bxd5 2.Rg8+ Bxg8 3.Ra8#, the Bishop interferes with the Queen's defense of g8, which causes the Bishop to abandon its defense of a8 to prevent 2.Rg8#
Aleksandr N. Pankrat'ev and Josip Varga
"Sahovski Glasnik", 1991
White to play and mate in four.
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This more modern position has a kind of symmetry to it, in that there are two different Plachutta devices which white may employ against black, depending on how black responds to the key 1. e3. This pawn must be eliminated because it defends the d4 pawn and threates 2.Rc5#. How should black respond? The side is on the horns of a dilemma, as no matter how black replies white will counter with a Plachutta.
- 1...Rxe3, avoiding the immediate checkmate of 2.Rc5, but white may now seek to checkmate with a Knight on either e3 or e5, if the defenses of the h-rank Bishop and Queen may be disrupted, respectively.
- 2.f4! Qxf4 3.Nxe3+ Qxe3 4.Nxe5#, here we see black's second move interfering with the Bishop, overloading the Queen, and abandoning any defense of the e5 square.
- 2.f4! Bxf4 3.Nxe5+ Bxe5 4.Nxe3#, here we see black's second move interfering with the Queen, overloading the Bishop, and abandoning any defense of the e3 square.
- 1...Bxe3, avoiding the immediate checkmate of 2.Rc5, but white may now seek to checkmate with a Knight on either e3 or b5, if the defenses of the aRook or the bRook may be disrupted, respectively.
- 2.Bb3+! Rbxb3 3.Nxe3+ Rxe3 4.Nb6#, here we see the bRook interfering with the aRook, overloading itself, and abandoning its defense of the b5 square.
- 2.Bb3+! Rbxb3 3.Nb6+ Rxb6 4.Nxe3#, here we see the aRook interfering with the bRook, overloading itself, and abandoning its defense of the e3 square.