Keen

Use every number from 1 to the board size exactly once in each row and column. The thick borders form cages. Combine all numbers in a cage with its shown operation to make the target.

6+: numbers add to 6. 6×: numbers multiply to 6. 2−: the larger minus the smaller is 2. 2÷: the larger divided by the smaller is exactly 2. A one-cell cage shows its number. Subtraction and division always have two cells.

Numbers may repeat inside a cage only if they are in different rows and columns. Cage colors are only a visual aid; thick borders and labels define the rule.

Select a cell, then tap a number. Notes pencils possibilities; turn Notes off to place a number. Erase clears a cell. Undo keeps the last 64 edits. A completed cage is checked only after all its cells have numbers, so an unfinished cage may still contain an error.

Keyboard: arrows select; digits place; N toggles Notes; U undoes; Delete clears; Escape deselects. No timer or answer-revealing hint. Historical completion is separate from the current board.