How to play Squirrels.

The rules.

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.

Your marks are your own, not the game's. A hollow can carry small marks in its corners, small marks in its middle and one of nine colours, all at the same time, and none of them ever turns 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.

Controls.

The same on a phone and on a keyboard, and the same in every ARLing number game.

• Moving about. Click or tap a hollow to pick it. Drag across the wood with the mouse or the finger to pick several at once. Ctrl (on a Mac Cmd) plus a click adds one to the picked hollows or takes it away, and Ctrl plus an arrow grows the picked patch. The arrow keys move from hollow to hollow and step over the edge of the wood to the other side; W A S D do the same. Escape lets the whole selection go.
• Writing. 1 to 9, on the number row or the numeric keypad, or the pad under the wood, write into every picked hollow at once; the same number again takes it back. Delete or Backspace clears in one order: the numbers first, then the marks, then the colour. A number written into a hollow that has marks covers them, and they come back when the number goes.
• The four modes. The buttons under the pad say what a number writes: Normal the big number, Corner a small mark in the corners, Centre a small mark in the middle, Colour one of nine colours. Z X C V pick one, the space bar walks round all four, N steps through the two kinds of mark and back. Holding Shift writes a corner mark and holding Ctrl a centre mark for that one number, without leaving the mode you are in. The nine colours run from dark to light with their number, so they can be told apart by brightness alone.
• Undo and Redo. Ctrl+Z or U goes back, Ctrl+Y, Ctrl+Shift+Z or R goes forward, as far as you like in either direction. Ctrl+R is left alone: that is the browser reloading the page.
• Restart. Every number, mark and colour comes off the wood. The clock keeps running and one Undo brings it all back; the game asks first, unless you turn that off in Settings.
• Check. Two presses. The first says how many numbers are wrong and which rows or columns they sit in, the second marks them. With a single hollow picked it looks only at the two runs through it. P pauses the clock and hides the wood.

Settings holds eleven switches and nothing more: Control method, Display timer, Highlight matching numbers, Cell selection when dragging, Number entry with noted cells, Highlight errors, Default note style, Auto remove restricted notes, Auto pause, Onscreen input only and Confirm before Restart.

A way in.

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.

The week.

Difficulty is measured, not guessed. Every wood is checked to be solvable by named rules alone; the candidates for a date are ranked by how much they lean on the harder ones.

This week