1. Trellis is a game for two players, Black and White, who alternately put stones of their color on the board. Once placed, stones do not move.
2. The board is a 15x15 checkered grid (counting the points rather than the squares), as shown in Diagram 1. The upper left square is a dark square. The board begins empty, and play takes place on the points.
Diagram 1 --- the board for playing Trellis
3. A turn consists of playing two stones, which must be exactly three points apart, in either an L-shape (i.e., the knight's relation) or in a straight line. For instance, if White plays the first stone of his turn on J11 as shown in Diagram 2, the second stone may be played on any of the points marked in orange. (It doesn't matter whether the intervening points are empty or occupied.) The lower left of Diagram 2 shows an example of a legal move by White, and the lower right of Diagram 2 shows an example of a legal move by Black.
Diagram 2 --- exactly three points apart
4. It is permissible to play just one stone, and it is permissible to pass.
5. It is not permissible to "mirror" the opponent's moves ten or more turns in succession.
6. The beginning of the game is governed by a "refined" pie rule. Player 1 plays two moves for Black and one move for White (a move can consist of up to two stones, of course). Player 2 then decides which side to take, with White to move. Note that the standard pie rule is encapsulated within the refined rule, because it is permissible to pass a turn. (I.e., Player 1 could play one move for Black, then pass for White, then pass for Black.)
7. Two same-color stones are considered to be connected if they're orthogonally adjacent, or if they're diagonally adjacent over a "home square." Black's home squares are the dark squares, and White's home squares are the light ones. Regard Diagram 3. The two black stones in the upper left are connected because they're orthogonally adjacent. The two white stones in the upper right are connected for the same reason. The two black stones in the lower left are connected, because they're diagonally adjacent over a dark square. The two black stones in the lower right are not connected, because they're diagonally adjacent over a light square, which is White's home color. To make the connection valid, Black must follow up with K3 or L4.
Diagram 3 --- connected vs. not connected
8. The object of the game is Hex-like. Black tries to connect the top and bottom sides of the board, and White tries to connect the left and right sides. A corner point is considered to belong to both sides that meet there. Diagram 4 shows an example of a winning connection for Black. The top of the board (at A15) has been successfully linked to the bottom (at H1). Note that A15 is considered to belong to both the left and top sides.
Diagram 4 --- a winning connection for Black
Trellis can be easily played with pen-and-paper. Simply mark an open circle for White and a closed circle for Black. Diagram 5 shows an example of a completed pen-and-paper game. White has won, successfully connecting the left side (at A13) to the right side (at O3).
Diagram 5 --- a completed pen-and-paper game