3139: Chess Variant

2025-09-09T10:32:51Z

2001:16B8:C73F:7100:667:594D:55E5:4100: /* Explanation */ Lined what that opening is called

{{comic
| number = 3139
| date = September 8, 2025
| title = Chess Variant
| image = chess_variant_2x.png
| imagesize = 310x344px
| noexpand = true
| titletext = The draw-by-repetition rule does a good job of keeping players from sliding a tile back and forth repeatedly, but the tiles definitely introduce some weird en passant and castling edge cases.
}}

==Explanation==
{{incomplete|This page was created recently by an IMMOVABLE CHESS BOARD. Don't remove this notice too soon.}}
A {{w|Sliding puzzle|sliding puzzle}} is a puzzle with movable pieces that challenges players to slide the pieces around the board to get them into a certain pattern or to move a certain piece into a certain position. Patterns can be anything from a completed image to a series of numbers. One of the most common variants, the {{w|15 puzzle}}, is a square board with 15 square pieces (usually numbered 1 through 15, to be placed in obvious order, but can also feature segments of a larger picture that needs to be correctly assembled) and one empty space in a 4×4 grid. The goal is to order the numbers (or reassemble the picture) without lifting any piece, only sliding adjacent pieces into the empty space. [[Randall]] contemplates making a {{w|Chess variant|variant of chess}} in which 2x2 sections of the board can be moved around, possibly as an alternative to moving your own pieces. It is possible that “sliding number chess puzzle” is a pun on actual {{w|chess puzzles}} in which pieces are set up in a position and the player must find the best move or sequence of moves in that position.

A similar concept exists in {{w|Three-dimensional_chess#Star_Trek_Tri-Dimensional_Chess|Star Trek 3D chess}}. Although there's no official rule set by the show creators, the rules were invented by Star Trek fans. In this variant, the board has several 2x2 "attack boards" that can be moved around. For a more prosaic analog, the game {{w|Labyrinth_(board_game)|Labyrinth}} uses a board composed of tiles that players use to rearrange the playing arena, and features a similar prohibition against reversing the change made by the previous play.

The title text states that because of the {{w|threefold repetition}} rule in chess, sliding a tile back and forth will result in a draw, just as would already happen with the moving of the ''pieces'' back into an overall state of the board. This may discourage unimaginative 'stalling' play by one player, in allowing the other player to claim a draw and avoid a loss. Also, with the tiles, ''{{w|en passant}}'' pawn capture and {{w|castling}} is weird, due to the possibility of having to decide whether moving a tile's squares counts as moving a piece. Moving certain pieces make them ineligible for castling, and effects whether a pawn is eligible for ''en passant'' capture, as well as where the capturing pawn goes after an ''en passant'' capture. It is also left unclear whether the wider-ranging pieces are allowed to effectively move through the missing/virtual spaces in the board where there currently is no tile, beyond merely being unable to ''end'' their move in the current 'hole' where no traditional chess squares exist at that moment.

One interpretation of the game shown is that white played e4, black e5, continuing with Nf3 and Nc6, then white played d4 (all normal moves, so far, the [https://lichess.org/opening/Scotch_Game Scoth Opening]). In response, black slid the puzzle-square starboard to make white’s knight on the rim 'dim', and decentralize white’s pawn.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
:[A chessboard is shown with the white pieces at the bottom of the screen. The pieces are illustrated in the basic design of standard computer chess. The chessboard is divided into 16 2x2 sliding squares with the e3-f4 sliding square currently being moved to the g3-h4 spot. Otherwise the opening is a standard Scotch Opening, with the pieces in the e3-f4 spot like how they are supposed to be]
:[Text below the panel]
:Sliding number puzzle chess

{{comic discussion}}<noinclude>

[[Category:Chess]]

explain xkcd - User contributions [en]

3139: Chess Variant