# Ta Yü — the ruleset to implement Ta Yü is a connection game by Niek (Nicolas) Neuwahl, published by Kosmos in 1999 and nominated for the Spiel des Jahres that year; Goliath reissued it in 2009. It is long out of print, which is why it is being rebuilt here. **This game is not implemented yet.** This document is the specification the engine will be written against, and it is deliberately explicit about which parts are attested by sources and which parts are reconstructed. Read the [Provenance](#provenance) section before treating any number here as gospel. Players lay 1×3 river tiles outwards from the centre of a large board. Each tile carries three river mouths, and a river mouth may never be walled off against the blank flank of another tile — so every placement is constrained by everything already down. One side is trying to run water out to the north and south edges, the other to the east and west. Scoring multiplies the two opposite edges together, so a river that reaches only one of your edges is worth nothing at all. ## Table - **Players — *toggle*.** Two or four. - **Two.** One player takes north–south, the other east–west. - **Four.** Two partnerships: seats 0 and 2 play north–south, seats 1 and 3 play east–west, so partners are never seated next to each other. - The three-player "flood" variant is **not** being implemented — see [Known gaps](#known-gaps). ## Board An **18 × 18** grid of cells. Rows are numbered from the north edge, columns from the west edge. Each of the four edges has 18 possible **exits** — one per edge cell — where a river can run off the board. Three exits on each edge are **marked** and count double. ``` north edge (row 0) ┌────────────────────┐ west │ │ east edge │ 18 × 18 │ edge │ │ └────────────────────┘ south edge (row 17) ``` ## Tiles 84 tiles, drawn blind from a bag. Each tile is **1 × 3** and carries exactly **three river mouths** on its perimeter, all joined to one another by channels across the face of the tile — so water entering any mouth can leave by either of the other two. A 1×3 tile has eight places a mouth can sit. Taking the tile lying east–west and its cells numbered 0, 1, 2 from the west: | Slot | Where | | --- | --- | | `N0` `N1` `N2` | north flank, above each cell | | `S0` `S1` `S2` | south flank, below each cell | | `W` | the west end | | `E` | the east end | Choosing 3 of those 8 gives 56 arrangements, and a tile can be turned end for end, which pairs them off: `N0↔S2`, `N1↔S1`, `N2↔S0`, `W↔E`. No arrangement is its own mirror under that turn, so the 56 collapse to exactly **28 distinct tiles**. **84 = 3 × 28.** The set is three copies of every tile that can exist. (The 1999 Kosmos edition had 112 tiles — 4 × 28 — and the reissue cut it to three copies each to shorten the game. Both counts landing on a whole multiple of 28 is the main reason to trust this reconstruction of the geometry.) Of the 28, **12 have their three mouths on three different flanks** of the rectangle, which matches the reissued tiles being marked with a concentric ring on the centre stud for exactly that case. The engine generates the set rather than listing it, so the tile table cannot drift out of step with the count. ## Turn 1. **Draw** one tile from the bag, face up. There are no hands and no hidden tiles — everyone sees what you drew, and the only concealed information in the game is the order of the bag. 2. **Place** it, in any of its four orientations (east–west or north–south, either way round). 3. If the drawn tile has no legal placement anywhere, it is **set aside** and the turn passes. It does not come back. ### Placing the first tile The opening tile must cover at least one of the four centre cells — (8,8), (8,9), (9,8), (9,9). Everything else grows out from it. ### Placing every tile after the first A placement is legal when all of the following hold. - **The three cells are empty** and lie in a straight line on the board. - **Every one of the tile's three mouths is accounted for.** Take each mouth in turn and look at what is on the other side of it: - *an empty cell* — fine, the river runs on into open ground; - *off the board* — fine, and that is a scoring exit (see below); - *a tile that has a mouth facing back* — fine, the two join up; - *a tile with a blank flank there* — **illegal**. A river may never dead-end against the side of another tile. - **The tile's blank edges must not wall anything off either.** If a blank part of the new tile lands against an existing tile's mouth, the placement is illegal, for the same reason read from the other direction. - **The tile must join the network.** At least one of its mouths must meet a mouth of a tile already on the board. Because every tile joins the network by at least one mouth, and because all three mouths of a tile are connected across its face, **everything on the board is always one single river system** running back to the opening tile. The engine gets connectivity for free and never has to trace it. ## End of the game The game ends when the bag is empty, or when no tile left in the bag can be placed anywhere. ## Scoring Count each side's exits — mouths that run off the board — on each of its two edges. - An ordinary exit counts **1**. - One of the three **marked** exits on that edge counts **2**. Then, for each side: ``` score = (exits on one edge) × (exits on the opposite edge) ``` North–south multiplies its north count by its south count; east–west multiplies east by west. **A side that reaches only one of its two edges scores nothing**, which is the whole tension of the game: breadth on one edge is worthless without a matching breakthrough on the other. Higher score wins. Equal scores are a draw. ### Where the marked exits sit Positions **3, 8 and 13** along each edge, counted clockwise from that edge's first cell, giving the board four-fold rotational symmetry so no side is better placed than another. This is a **choice, not a reproduction** — see below. ## Provenance Everything above is reconstructed from secondary sources. The rulebook itself could not be reached from this machine: outbound web requests are blocked by the environment's network policy, so only search-result summaries were available, and BoardGameGeek's rules files were out of reach entirely. **Attested by sources:** designer and year; 84 tiles in the reissue and 112 in the original; 1×3 tiles with three connections each; the board's round indentations and the opening tile going in one of the four centre ones; the mouth-accounting placement rule and the ban on a river ending against a blank; north–south versus east–west; the multiplicative scoring; marked exits counting double, three to a side; the game ending when nothing can be placed; the three-player flood variant existing. **Reconstructed here, and the parts to check against a real copy:** - **The board is 18 × 18.** One source describes the physical board as having 18 × 18 indentations; several others say 19 × 19. 18 × 18 is used because it is the one that makes "the four centre indentations" true — a 19 × 19 grid has a single centre cell, not four. If a rulebook ever settles this the other way, `BOARD_SIZE` is the only number that has to change. - **The 28-tile set and its geometry.** Derived, not read off a component list. It is trusted because 84 and 112 are both exact multiples of 28, and because 12 of the 28 touch three flanks, matching the ringed tiles in the reissue. - **All three mouths on a tile interconnect.** Consistent with every description found, but not stated outright anywhere. - **The marked exits at 3, 8 and 13.** Their real positions are unknown. Three mirror-symmetric marks are impossible on an even-length edge, so the real board cannot be reflectively symmetric per side either; a rotationally symmetric layout was picked as the fairest guess. This is cosmetic to the rules and structural only to the final score. - **An unplaceable drawn tile is set aside and the turn passes.** The alternative reading is that the game simply ends there. This is the same posture as the Sequence board layout: where the real thing could not be verified, ship an honest substitute and say so, rather than a guess dressed up as authentic. ## Known gaps - **The three-player flood variant is not implemented.** Sources agree it exists and that the third player tries to stop the other two reaching the edges, but nothing found says how the flood *scores*, and inventing a scoring rule would be making up a different game. Two- and four-player tables cover the family case; this can be added if the rulebook turns up. - **No draw-a-replacement rule.** A tile that cannot be placed is gone for good rather than swapped, which is the simpler of the two readings.