A Takuzu grid holds two kinds of piece. Never three alike in a row, the same number of each in every line and column, and no two lines identical — nor two columns. The second form adds signs between neighbouring cells: = means alike, × means different.

• 10solving techniques, in five levels
• 5grid sizes, 6×6 to 14×14
• 3steps to a hint

The solver never guesses

It applies the easiest technique that works, and a grid's level is the hardest one it had to reach for. A grid the logic cannot finish is thrown away rather than shipped. The back-tracking code exists, but only to check off-screen that a grid has exactly one solution — the player never meets it.

A hint points before it plays

Where to look, then which technique applies there, then the move itself. If you have already placed a piece that cannot be right, the hint says that first instead.

Why the no-identical-lines rule stays

Some versions drop it. Keeping it is what makes several of the techniques possible, and it is a rule of the puzzle rather than a deduction from the answer being unique.

Seven languages, nine variants: English, French, German, Spanish (Spain and Latin America), Italian, Japanese and Portuguese (Brazil and Portugal).

This one is honest about where it stands: the engine is written and the nine languages are in place, but the grid bank has not been produced and there is no game to play yet — no board, no screens, no icon. It is a skeleton, and this page will grow when it becomes a game.