Rivers laid out from the centre of an 18x18 board on 1x3 tiles, each with
three mouths that must line up with whatever they touch. One side runs water
north and south, the other east and west, and a side's score is one edge
multiplied by the other — so reaching only one of your two edges is worth
nothing, which is the whole tension of the game.
Two things fell out of the geometry rather than needing to be tabulated. The
tile set is generated: three mouths chosen from the eight places one can sit
on a 1x3 tile gives 56 arrangements, turning a tile end for end pairs them
off with none fixed, so there are exactly 28 distinct tiles and the box's 84
is three of each. And because every tile joins the network by a mouth while
all three of its own mouths interconnect, the board is always one connected
river system — so scoring never traces connectivity, and a mouth at the edge
is an exit by construction. Both properties are asserted over whole games.
The placement check is one comparison doing two jobs: where a new tile abuts
an old one, both sides must agree. That refuses a river dead-ending against
stone and, read the other way, refuses a blank flank that would wall off a
river already down.
18x18 comes out under 20dp a cell on a phone, too fine to tap, so laying a
tile is a tap to line it up and a button to commit. Tapping the same cell
again cycles the other legal ways the tile could cover it, which is also how
it gets turned — a rotate control would have landed on illegal positions. A
tap on a cell the tile cannot cover is ignored rather than treated as a
deselection, so a fingertip one cell wide of the mark does not throw away a
placement.
Two AI settings, not three. A blocking-heavy variant was written and dropped
because it played the full setting dead even over 30 games; shipping it as a
step up would have been a claim that could not be backed. What ships is held
to measured numbers: full strength won 20 of 20 against random placement from
either axis, gentle beats random about three games in four and loses to full
strength about four in five, and random against random comes out even, which
is what makes the rest of those numbers mean anything.
The reconstruction's uncertainties stay called out in the rules doc rather
than being smoothed over now that the code exists: the 18x18 board reading,
the marked exits placed at 3, 8 and 13 by choice, and the three-player flood
variant left out because nothing found says how the flood scores.
Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_015pyhC1KyFkQk6hUnnX2Tof
Ta Yü has been out of print since the 2009 Goliath reissue, so the rulebook
had to be reconstructed from secondary sources — and this machine's network
policy blocks everything but search summaries, so BGG's rules files were out
of reach too.
The tile set fell out of the geometry rather than needing a component list.
A 1x3 tile has eight places a river mouth can sit; three mouths chosen from
eight gives 56 arrangements, and turning a tile end for end pairs them off
with no arrangement fixed, leaving exactly 28 distinct tiles. The reissue
has 84 tiles and the 1999 original had 112 — 3x28 and 4x28. Twelve of the 28
touch three flanks of the rectangle, which is what the ringed centre stud on
the reissued tiles marks. Three independent numbers agreeing is why the
geometry is worth trusting.
What could not be pinned down is called out in the doc rather than smoothed
over: the board is taken as 18x18 because that is the reading under which
"the four centre indentations" is true, the marked exits are placed at 3, 8
and 13 by choice, and the three-player flood variant is left out entirely
because nothing found says how the flood scores, and inventing that would be
shipping a different game. Same posture as the Sequence board layout.
The catalogue entry is added with available = false, so it shows as coming
soon on dev builds and stays out of production until the engine lands.
Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_015pyhC1KyFkQk6hUnnX2Tof
Claude