# Rules of play **Version:** v011 — Piece Type Drift on Arrival This document completely describes how to play this version of the game. A reader with only this document and the interface can play a full game against another player, and the two of them can determine who won. ## The game Hexagonal chess, after Wladyslaw Glinski. Two players, White and Black, share one screen and take turns with the same pointer. The board is not a square grid: it is a large hexagon tessellated into **91 hexagonal cells**, arranged in eleven vertical files. Cells come in three tones, repeating across the board, which mark the three colour bounds a bishop can never leave. **Files and ranks.** The eleven files are lettered **a b c d e f g h i k l** from left to right — the letter *j* is skipped, as in Glinski's own notation. The files have different heights: 6, 7, 8, 9, 10, 11, 10, 9, 8, 7, 6 cells, so the outer files are short and the central f-file is the tallest. Within each file the cells are numbered **from 1 upward starting at the White (bottom) end**. A cell is named by its file letter and its number: `a1`, `f11`, `k7`. Ranks can reach two digits (`e10`, `f11`). White moves first. Players alternate, one move per turn. Passing is not allowed. ## Starting position Each side has eighteen pieces: one king, one queen, two rooks, two knights, **three bishops**, and **nine pawns**. White's pieces stand on: - **King** g1, **Queen** e1 - **Bishops** f1, f2, f3 (stacked on the central file, one on each of the three cell tones) - **Knights** d1, h1 - **Rooks** c1, i1 - **Pawns** b1, c2, d3, e4, f5, g4, h3, i2, k1 (a shallow chevron across the board) Black's position is the exact 180° rotation of White's through the centre cell f6, so the two armies are perfectly symmetric. The interface sets up the board; you do not place pieces by hand. ## Objective Checkmate the opposing king: attack it so that the opponent has no legal move that removes the attack. Delivering checkmate wins the game immediately. Kings are the one piece the renaming rotation never touches (see **Piece renaming**), so a king is always present and always findable, and checkmate stays reachable. Check and checkmate are computed from the pieces as they currently stand on the board — that is, by their renamed types — not by the types the move list names them. ## Adjacency Every cell has two kinds of neighbour: - **Six orthogonal neighbours** — the six cells that share an *edge* with it. These are the rook directions. Within a file, the orthogonal neighbours directly above and below are the same file, one rank up or down. - **Six diagonal neighbours** — the six cells that share only a *vertex* with it. These are the bishop directions. A bishop direction always keeps a piece on cells of a single tone; a rook direction moves between tones. ## Piece movement - **Pawn** (circle): moves one cell straight forward — toward the opponent's side — to an empty cell. It never moves two cells, and it never moves backward. It captures onto either of the **two forward diagonal cells** (the diagonal neighbours to the forward-left and forward-right). White's forward is up the board; Black's is down. - **Knight** (L shape): leaps to one of up to twelve cells — the cells reached by one orthogonal step followed by one diagonal step outward, so that the leap lands on neither a rook line nor a bishop line from its origin. It jumps over anything in between. - **Bishop** (triangle): moves any number of empty cells along a diagonal (vertex-sharing) direction. Confined for the whole game to cells of its one tone. - **Rook** (square): moves any number of empty cells along an orthogonal (edge-sharing) direction. - **Queen** (asterisk): moves any number of empty cells along any orthogonal or diagonal direction. - **King** (cross): moves one cell to any of its **six orthogonal neighbours**. A piece captures by moving onto a cell occupied by an enemy piece, which is removed. No piece except the knight may pass through an occupied cell. You may never capture your own piece. ## Piece renaming Each time a piece completes a move, its type is reassigned the instant it arrives, following a fixed rotation: - a **queen** becomes a **rook**, - a **rook** becomes a **bishop**, - a **bishop** becomes a **knight**, - a **knight** becomes a **pawn**, - a **pawn** becomes a **queen**. **Kings are never renamed.** Every other piece is subject to the rotation. The reassignment takes effect on arrival, before your opponent moves: the piece's appearance changes to the new type at once, and from that point on the piece moves, captures, gives check, and can be checkmated as the new type — a pawn that has just arrived and become a queen moves as a queen on its next turn. Nothing announces the change; there is no prompt, no highlight, and no entry in the move list calling attention to it. The reassignment is applied by the side to move's own move: it is the mover's arriving piece that is renamed, not the opponent's. A capture renames the capturing piece (the captured piece is simply removed as usual). Piece counts and type distributions are **not** maintained: there is no limit of one queen or two rooks per side, and a board may carry any number of pieces of any type as successive renames accumulate. The starting position (above) is unchanged — renaming begins only once a move is made. Because the move list records each move by the type the piece *was* when it left, and the board shows the type it *became* on arrival, the written move list and the position on the board describe each other only loosely: the list, read as a text, will name a piece by one type in the move that placed it and by another type in its next move. This is intended. To know what a piece is now, read the board, not the list. ## Promotion A pawn that reaches the **far edge** — the border of cells on the opponent's side, from which it could advance no further — promotes at once to a queen, rook, bishop, or knight of its own colour, at its owner's choice. The interface presents the choice when it occurs. The move list records the promotion you chose (`=Q`, `=R`, `=B`, or `=N`); then the renaming rotation applies to the promoted piece as to any arrival, so the piece on the board is one step along the rotation from the type you selected (a pawn promoted to a queen arrives as a rook). ## Special moves that do not exist here There is **no castling**, **no en passant**, and **no two-cell pawn advance**. These moves of square chess have no counterpart in this version. ## Check and legality A king is **in check** when an enemy piece attacks its cell. You may never make a move that leaves your own king in check; the interface enforces this by offering only legal moves. If you are in check, every legal move available to you resolves the check. ## How a game ends The interface detects each of these conditions automatically and announces the result in the status line. That announcement is the authoritative verdict. **Decisive result:** - **Checkmate.** The player to move is in check and has no legal move. That player loses; the other player wins. **Draws (neither player wins):** - **Stalemate.** The player to move is not in check but has no legal move. - **Fifty-move rule.** Fifty consecutive full moves pass with no capture and no pawn move. - **Threefold repetition.** The same arrangement of pieces, with the same player to move, occurs for the third time. - **Insufficient material.** Neither side retains enough material to ever deliver checkmate — king against king, king and a single knight or bishop against king, or kings with only bishops that all stand on one colour tone. ## Determining the winner Play until the status line announces a result. "Checkmate — White wins" or "Checkmate — Black wins" names the winner. "Stalemate" or "Draw" means neither player has won. The verdict is computed from the position and displayed; it is always definite. Checkmate is reachable — Glinski's hexagonal chess has been played to decisive results for decades — so the game always terminates in one of the announcements above. ## The interface Move by dragging a piece to a highlighted destination, or by clicking a piece and then clicking a destination. When a piece is selected, its legal destinations are marked: empty destinations are shaded, and a cell you can capture on is ringed. **New game** starts over; **Undo** takes back the most recent move by agreement of the players. The game is local: both players share one screen. **Forced moves.** When the player to move has exactly one legal move, that move executes automatically after a short delay, with no announcement. It appears in the move list identically to a hand-played move. The delay is a decaying floor: the first auto-execution in a game waits 800 ms, and each subsequent auto-execution waits 50 ms less than the one before, down to 0 ms — reached after sixteen consecutive auto-executions and held there for every one after. The countdown runs down across the whole game session and across both players; it is never displayed. Because a whole sequence can consist of successive forced positions, this may advance several moves in a row without any input, each a little faster than the last. Auto-execution never changes which move is legal or how the game ends; it only removes the wait when there is no choice to make. If **Undo** returns the game to a position where the side to move still has only one legal move, that move executes again after the current delay. The guarantee holds however the forced position is reached — by ordinary play, by **Undo**, or by editing the move list (below): whenever the side to move has exactly one legal move, that move executes after the current delay. **New game** starts a fresh decay sequence, restoring the delay to 800 ms. **The move list.** Each move is recorded in this version's coordinate notation — the piece letter (none for a pawn) followed by the destination cell, with `x` for a capture and `=Q`/`=R`/`=B`/`=N` for a promotion. Each entry in the list is editable in place, a carry-over from the square version. Editing replays the list from the start; because the notation here is hexagonal rather than standard algebraic, an edited entry that the replayer cannot interpret — and every entry after it — is struck through as unreachable, and the board shows the last position actually reached. Playing by pointer, rather than by editing the list, is the reliable way to reach a position in this version. A game whose move list has been edited is not saved across a page reload. Editing the list replays the moves *without* applying the renaming rotation, so immediately after an edit the board shows the un-renamed types; renaming resumes on the next move played by pointer. Reaching a position by ordinary play, where each arrival is renamed, is the way to see this version as intended.