How to play Squirrels.

1. Squirrels hide acorns in the hollows. Each sign tells how many acorns are in the run of hollows to its right or below it. A run is the unbroken line of hollows that follows a sign, and it ends at the next trunk or the edge of the wood.

2. Every hollow holds 1 to 9 acorns. Every hollow belongs to one run across and one run down at the same time, and no number repeats within a run. That is where the puzzle lives: the number you write has to suit both runs.

3. Every wood has exactly one arrangement that fits every sign. When the last hollow is right, the game notices by itself.

Notes are your own, not the game's. Notes switch the pad to the small numbers you keep while you think; they never turn red while you play. Only Check judges, and only when you ask, in two steps: it first says how many numbers are wrong and which rows or columns they sit in, then, on a second press, marks them.

A wrong number is shown by Check, never by the board turning red while you play.

Every wood opens with steps like these. Hint finds the next one for you, outlines the two runs through the hollow it means and says why; press it again to write the number in. Hints are counted and shown when you finish, never hidden.

• A run with one hollow left. Its total minus what is already there settles the last number.
• A total with only one way to make it. Two hollows adding to 3 can only be 1 and 2; to 16, only 7 and 9. Three hollows adding to 6 are 1, 2 and 3.
• What both runs still allow. The run across and the run down through a hollow narrow the numbers that fit; sometimes only one is left.
• A number a run has to use. When it fits only one of the run's hollows, that is where it goes, even if that hollow could still hold other numbers on its own.