How to play Hedgehogs.

1. Two hedgehogs in every row, every column and every flowerbed. The flowerbeds are the outlined shapes. A garden with eight rows has eight columns and eight flowerbeds, so sixteen hedgehogs in all; nine by nine has eighteen, ten by ten has twenty.

2. No two hedgehogs may touch. Not side by side, not diagonally. They prickle. So every hedgehog keeps the eight cells around it empty.

3. A dot is your note that a cell stays empty. Dots are yours; the game does not judge them, except when you ask with Check. When the last hedgehog is placed, the game checks the whole garden by itself.

They prickle. Place a hedgehog and the eight cells around it are settled: dots go there. If a second hedgehog lands next to it, even at a corner, the game turns both red. The second hedgehog of that row or column sits at least one cell away.

On the phone, hold your finger and drag to sweep dots over several cells. On a keyboard, arrows move, X is a dot, H a hedgehog, Delete clears, P pauses.

Every garden opens with steps like these. Hint finds the next one for you, outlines the row, column or flowerbed it is looking at, marks the cells that follow and says why; press it again to fill them in. Hints are counted and shown when you finish, never hidden.

• A full line. Once a row, column or flowerbed holds its two hedgehogs, every other cell in it is a dot.
• Exactly enough room. A line that still needs two hedgehogs and has exactly two cells left where they fit: both are hedgehogs.
• A flowerbed inside one row. If all the free cells of a flowerbed lie in one row (or column), the flowerbed's hedgehogs use up that row, so the rest of the row is dots. Two flowerbeds inside two rows work the same way.
• Common neighbours. Look at every way the remaining hedgehogs of a line can be placed. A cell that touches a hedgehog in every one of those ways stays empty.