# Reading moves

This application uses a custom notation for its three shogi variants. It is not KIF, SFEN, or USI. The labels make moves readable; use the exported game JSON to save or exchange a complete replay, including its route and facing information.

## Squares and owners

Files are labelled `a` through `i`. Ranks increase from bottom to top in the default chart view: `1`–`11` on the Möbius board, `1`–`18` on the Klein board, and `1`–`9` on each genus-two sheet. A square such as `e4` means file e, rank 4.

Genus-two coordinates always include the sheet: `I:a4` and `II:a4` are distinct squares. Use the displayed rank labels on each sheet. Joined edges can connect squares with surprising labels; coordinates alone do not describe the path between them.

The history shows an owner marker alongside each move: **▲ Black** (owner A) or **△ White** (owner B). Ownership is independent of facing. A piece that turns at a reflected seam keeps its owner.

## Pieces and symbols

| Symbol | Meaning |
| --- | --- |
| `K` | King |
| `R` | Rook |
| `B` | Bishop |
| `G` | Gold |
| `S` | Silver |
| `N` | Knight |
| `L` | Lance |
| `P` | Pawn |
| Prefix `+` | The moving piece was already promoted, for example `+P`. |
| `–` | Move to an empty square. |
| `×` | Capture the piece on the destination square. |
| Suffix `+` | Promote on this move. |
| Suffix `=` | Decline an available promotion. |
| `*` | Drop a piece from the hand. |
| `↑` or `↓` | Changed facing: now toward higher or lower displayed ranks, respectively. |

A board move contains the piece, origin, destination, and any promotion or facing change. For example, `P e9–e10+` promotes a pawn, while `+P e10–d10` moves a pawn that is already promoted. A move outside the promotion conditions has neither `+` nor `=` as a suffix.

A drop gives the piece and destination, such as `P*c4`. Drops are always unpromoted. Black drops facing toward higher ranks and White toward lower ranks; the drop label does not add a facing arrow.

Facing arrows appear only when the move changes facing. Their absence means the piece retained its previous facing, not necessarily that it faces toward higher ranks. They do not mean check. The history labels do not append a check or checkmate symbol; the game status reports those conditions separately. The letter `K` means king, not check.

## Examples from the lessons

Each example below is produced by an actual legal action in the corresponding lesson position.

| Label | What happened |
| --- | --- |
| `P e3–e4` | Black’s pawn makes its first move on the Möbius starting board. |
| `R e2×e5` | A rook captures the opposing piece on e5. The captured type enters the rook owner’s hand, without promotion. |
| `G i4–a8 ↓` | A gold crosses the Möbius side seam and now faces toward lower ranks. |
| `G a8–b7` | That same gold moves diagonally forward, retaining its lower-rank facing. |
| `P e9–e10+` | A pawn chooses promotion on the Möbius board. |
| `+P e10–d10` | The promoted pawn moves sideways using gold movement. |
| `P*c4` | The pawn captured earlier in the exercise is dropped on c4. |
| `P*d4` | A pawn is dropped on d4; the lesson’s existing pawn on file c prevents a drop on that file. |
| `R e18–e1` | A Klein rook crosses the joined top and bottom edges without changing facing. |
| `R a5–a14= ↓` | A Klein rook reaches a14 through the reflected side seam, declines promotion, and reverses facing. |
| `P I:a4–II:a4` | A genus-two pawn crosses to the other sheet in one forward step. |
| `G I:d4–I:e5` | A gold follows a legal diagonal at an ordinary bend of the genus-two seam. |
| `N I:a3–I:i5` | A genus-two knight follows the forward–sideways–forward jump convention. |
| `G d2–e2` | A gold blocks a rook’s check in the king-safety lesson. |

The Klein rook can also reach a14 from a5 while preserving its facing. The destination alone therefore does not identify the intended outcome. Select the promotion and final-facing choice when the application offers alternatives. The displayed path illustrates the engine’s chosen route; the readable label does not list every traversed square.

For movement, promotion camps, drop restrictions, and game endings, see the [complete rules](./rules.md).