The numbers beside each row and above each column tell you the lengths of the filled runs in that line, in order. 3 1 means a run of three, then at least one gap, then a single cell — somewhere in that line.

Cross out the cells you have ruled out; they are what turns a maybe into a certainty. Every board here is checked before you see it, so it can always be finished by reasoning alone — there is never a point where you have to guess.

• ← ↑ ↓ →move
• Spacefill
• Xcross out
• Zundo
• Nnew puzzle