Switch-Side Chain-Chess

Introduction The Concept of a Chain Rules & Game Notation Notes

Introduction

In 1965, in analogy to the fruit fly as used in early genetics, chess was described by the Russian mathematician Alexander Kronrod as the Drosophila of artificial intelligence (AI). I developed a new variant of the game that perhaps serves as a greater challenge to AI while retaining many aspects of the game that have already been studied well. 'Switch-Side Chain-Chess' (SSCC)^[1] was created and features a simple rule that either player has the right to switch sides with the opponent should the piece he just moved form a 'chain' on the board. The variant can be played on any standard international chess set, although a board that allows for easy rotation would be preferable. A standard chess set and turntable device would also suffice.

The Concept of a Chain

A 'chain' in SSCC constitutes:

a) a continuous link of pieces of any color completely surrounding at least two adjacent empty squares;
b) such that if a line was drawn following the pieces, it would pass through each only once;
c) and the piece that moved last must be part of the chain.

(a). Simple chain.		(b). Expanded chain.
(c). A chain with diagonally adjacent empty squares.		(d). Flexibility of a chain to be expanded or contracted.

Figure. 1 shows several examples of chain configurations. In (a), if an additional piece is placed on d7 it would not create a chain because I would have to pass through the d6 square twice to complete the circuit. In (b), I see how a chain can be expanded by adding a piece (the knight on b5) to an existing chain. In (c), the two diagonally adjacent empty squares in the center of the chain are also valid. In (d), a piece already in an existing chain (the black king) can either expand it by moving from e5 to e6 or contract it by moving from e6 to e5, forming a new chain.

The largest chain, in terms of 'area', would constitute 28 pieces stretching along the four edges of the board whereas the smallest chains would consist of 6 pieces and resemble (a) or (c) in Figure. 1. It follows that, with fewer than 6 pieces on the board, SSCC reverts back into the standard version's endgame as no more chains are possible, and thus no more switching.

Consider the constructed position in Figure 2 more carefully. The move Qd3 gives White the option of switching sides but there are at least four unique chains created as a result. These include d3-e4-d5-c6-b5-a4-b3-c3-d3, d3-e4-f5-g4-g3-f2-e2-d3, d3-e4-f5-g6-g7-f8-e7-d6-c6-b5-a4-b3-c3-d3, and d3-e2-f2-g3-g4-f5-g6-g7-f8-e7-d6-c6-b5-a4-b3-c3-d3. In a game, especially under time controls a human player might miss spotting a chain and therefore the opportunity to switch sides; drawing or losing an otherwise won game.

Figure 2. Creation of several chains by Qd3.

Rules & Game Notation

When a chain has been created on the board and can be pointed out by the player who made the move, he has the right to switch sides with the opponent. If he chooses to do so, the turn is then his again as it would be in any case (the two armies alternate in their turns, as per the standard rules). Clocks (e.g. in tournament games) should be unaffected by the switching rule to prevent either player from waiting until the last second on his clock to switch. So in switching sides, you also inherit your opponent's time left.

If you are losing, there may be a way to trick or even force your opponent into creating an opportunity for you to create a chain on the board and assume control of his army in exchange for yours. If you are winning, you need to be mindful of such plans, beyond the regular concerns of the game. Consider the partial game of SSCC shown in Table 1. The 'S' columns indicate a 'switch' and are to be ticked where applicable in recorded games. The first four moves are nothing spectacular and would resemble a game between two non-experts in standard chess. See Figure. 3.

Table 1. A Partial Game of SSCC

Figure 3. Position after the first four moves.

Player A responds with the unexpected 5. c3!! This seemingly unpredictable move now leads to a forced mate. With White's 5^th move, a valid chain is created in his own army in order to switch sides. Player A now assumes the black pieces and proceeds as shown in Table 2 with 5. ... d4!, switching again. Notice the tick in the rightmost 'S' column of move 5.

Player A is now with the white pieces as before. He is able to create a series of chains and chooses to continuously switch sides until it leads to the inevitable checkmate on move 11 with the black pieces (see Figure. 4). Note that the chain after 10. Kd1 may not be immediately obvious, even though it is a relatively big one. An easy way to tell which color pieces a player currently has is to count the number of ticks on each side before and including the last move. If the ticks are even on each side, the players have their starting colors. Otherwise they control the opponent's army at the time. So in this game, with an uneven number of ticks, Player A wins and happens to do so with the black pieces.

Table 2. A Partial Game of SSCC (continued)

Figure 4. Final position after the last move.

Notes