How to play Beavers.

1. Every tree gets one beaver lodge right beside it, above, below, left or right. Each lodge belongs to one tree only, so there are as many lodges as trees.

2. Lodges never touch each other, not side by side and not corner to corner.

3. The number by each row and each column says how many lodges that line holds.

Exactly one arrangement fits. A line whose number is reached has grass everywhere else, and a tree with a single free cell beside it has its lodge there.

Grass is your own note that no lodge goes in a cell; only the lodges count. Tap a cell once for grass, twice for a lodge, three times to clear it. On the phone, hold your finger and drag to sweep the same mark over several empty cells. On a keyboard, arrows move, X puts grass, B a lodge, Delete clears, P pauses.

Nothing turns red while you play. Check, pressed once, says how many marks are wrong and roughly where; pressed again, it shows which.

Every pond opens with steps like these. Hint finds the next one for you: the first press says where to look and outlines the tree or the line, the second marks the step, explains it and fills it in. Hints are counted and shown when you finish, never hidden.

• A zero or a full line. A line whose number is reached is grass everywhere else, and a cell with no tree right beside it is always grass.
• A tree with little room. A tree with only one free cell beside it has its lodge there.
• Around a lodge. The eight cells around a lodge are grass.
• A whole line at once. Try every way to fit the lodges a line still needs, never two side by side. A cell that every way uses is a lodge; a cell that no way uses is grass.
• What a line touches. When every way to fit a line's lodges touches the same cell of the next line, that cell is grass. From Wednesday on, these two steps carry most ponds.