diff --git a/src/net.py b/src/net.py
new file mode 100644
index 0000000..9ddb893
--- /dev/null
+++ b/src/net.py
@@ -0,0 +1,178 @@
+"""
+Kernlogik des Spiels
+"""
+
+from enum import IntEnum, auto
+
+type Coordinate = tuple[int, int]
+
+
+class PieceType(IntEnum):
+    T_JUNCTION = auto()  # Direction is the piece at the "stem" of the T
+    STRAIGHT = auto()
+    CORNER = auto()  # Direction is the more counter-clockwise connection
+    NODE = auto()
+
+
+class Direction(IntEnum):
+    UP = auto()
+    LEFT = auto()
+    DOWN = auto()
+    RIGHT = auto()
+
+    @staticmethod
+    def from_offset(dx: int, dy: int) -> Direction:
+        if (dx != 0 and dy != 0) or abs(dx + dy) != 1:
+            raise ValueError(f"({dx}, {dy}) is not a valid direction offset")
+        if dx != 0:
+            return Direction(dx % 4)
+        else:
+            return Direction(dy + 1)
+
+
+class Piece:
+    type: PieceType
+    direction: Direction = Direction.UP
+    locked: bool = False
+
+    def __init__(self, type: PieceType) -> None:
+        self.type = type
+
+    def connected_directions(self) -> list[Direction]:
+        match self.type:
+            case PieceType.NODE:
+                return [self.direction]
+            case PieceType.CORNER:
+                return [self.direction, Direction((self.direction + 1) % 4)]
+            case PieceType.STRAIGHT:
+                return [self.direction, Direction((self.direction + 2) % 4)]
+            case PieceType.T_JUNCTION:
+                return [
+                    self.direction,
+                    Direction((self.direction + 1) % 4),
+                    Direction((self.direction - 1) % 4),
+                ]
+
+    def turn_cw(self) -> None:
+        self.direction = Direction((self.direction + 1) % 4)
+
+    def turn_ccw(self) -> None:
+        self.direction = Direction((self.direction - 1) % 4)
+
+
+DEMO_FIELD = [
+    [
+        Piece(PieceType.NODE),
+        Piece(PieceType.NODE),
+        Piece(PieceType.T_JUNCTION),
+        Piece(PieceType.NODE),
+        Piece(PieceType.NODE),
+    ],
+    [
+        Piece(PieceType.STRAIGHT),
+        Piece(PieceType.NODE),
+        Piece(PieceType.T_JUNCTION),
+        Piece(PieceType.STRAIGHT),
+        Piece(PieceType.CORNER),
+    ],
+    [
+        Piece(PieceType.T_JUNCTION),
+        Piece(PieceType.T_JUNCTION),
+        Piece(PieceType.T_JUNCTION),
+        Piece(PieceType.T_JUNCTION),
+        Piece(PieceType.NODE),
+    ],
+    [
+        Piece(PieceType.STRAIGHT),
+        Piece(PieceType.NODE),
+        Piece(PieceType.T_JUNCTION),
+        Piece(PieceType.T_JUNCTION),
+        Piece(PieceType.NODE),
+    ],
+    [
+        Piece(PieceType.NODE),
+        Piece(PieceType.NODE),
+        Piece(PieceType.CORNER),
+        Piece(PieceType.CORNER),
+        Piece(PieceType.CORNER),
+    ],
+]
+
+
+class Grid:
+    pieces: list[list[Piece]]
+    width: int
+    height: int
+
+    def __init__(self, width: int, height: int) -> None:
+        self.height = height
+        self.width = width
+        self.pieces = (
+            DEMO_FIELD  # TODO: Field generation or import from Tatham's version
+        )
+
+    def neighbors(self, x: int, y: int) -> list[Coordinate]:
+        neighbors: list[Coordinate] = []
+        for dx, dy in ((-1, 0), (1, 0), (0, -1), (0, 1)):
+            if (
+                x + dx < 0
+                or x + dx >= self.width
+                or y + dy < 0
+                or y + dy >= self.height
+            ):
+                continue
+            neighbors.append((x + dx, y + dy))
+        return neighbors
+
+    def solved(self) -> bool:
+        connected = [([False] * self.height) for _ in range(self.width)]
+        connected = self._solve_floodfill(0, 0, connected)
+        return all(map(lambda x: all(x), connected))
+
+    def _solve_floodfill(
+        self, x: int, y: int, connected: list[list[bool]]
+    ) -> list[list[bool]]:
+        connected[x][y] = True
+
+        connectedNeighbors: list[Coordinate] = []
+        for nx, ny in self.neighbors(x, y):
+            dx = x - nx
+            dy = y - ny
+            if (
+                Direction.from_offset(-dx, -dy)
+                in self.pieces[x + dx][y + dy].connected_directions()
+            ):
+                connectedNeighbors.append((x + dx, y + dy))
+
+        for nx, ny in connectedNeighbors:
+            if connected[nx][ny]:
+                continue
+            connected = self._solve_floodfill(nx, ny, connected)
+
+        return connected
+
+
+class NetGame:
+    _grid: Grid
+
+    def __init__(self, width: int, height: int) -> None:
+        self._grid = Grid(width, height)
+
+    def get_field(self) -> list[list[Piece]]:
+        return self._grid.pieces
+
+    def get_piece(self, x: int, y: int) -> Piece:
+        return self._grid.pieces[x][y]
+
+    def turn_cw(self, x: int, y: int) -> None:
+        self._grid.pieces[x][y].turn_cw()
+
+    def turn_ccw(self, x: int, y: int) -> None:
+        self._grid.pieces[x][y].turn_ccw()
+
+    def solved(self):
+        return self._grid.solved()
+
+
+g = NetGame(5, 5)
+print(g.solved())