Step 5 of 5
Lookahead
When nothing is forced, try a symbol in your head and see what breaks.
The rule of thumb: Try a symbol in your head: if one more forced move would break a rule, the cell must be the other symbol.
Sometimes no pair, gap, count or sign gives you anything. Then pick an empty cell and ask: what if this were a sun? Follow one forced move from there, using any of the four techniques you know.
If that one move breaks a rule (three in a row, four of a symbol in a line, a sign contradicted, or a cell forced both ways), a sun was impossible. The cell is a moon, and you know it for certain. That isn’t guessing: you only write down what you proved.
One step is enough on every board here. If your test needs a long chain before anything breaks, try a different cell.
Where to look: Lines that already hold two of one symbol, and cells touching a sign. A wrong symbol there runs into trouble fast.
Worked example
A real position from a board that needs Lookahead. Purple: what the reasoning rests on. Dashed: the cell in question. Green: what it proves (“this cell” in the text). Amber and red: what the tried symbol would force, and the rule it breaks.
That’s the whole track. Every Hard board here is solvable with these five techniques. Go find one. Play a Hard board →