How to play
- Fill every cell with a sun ☀️ or a moon 🌙.
- No more than two of the same symbol next to each other in a row or column.
- Three of each: every row and every column has exactly three suns and three moons.
- = means same, × means different. Cells joined by = hold the same symbol; cells joined by × hold opposite symbols.
Shaded cells are givens and can’t be changed. Sun and moon are different shapes, so you never need to tell them apart by color.
Controls
| Action | Touch / mouse | Keyboard |
|---|---|---|
| Cycle a cell | Tap: sun → moon → empty | Space or Enter |
| Sun | Tap once | S or 1 |
| Moon | Tap twice | M or 2 |
| Clear | Tap a third time | Backspace, Delete or 0 |
| Move around | – | Arrow keys, Home, End |
| Undo | Undo button | Ctrl/⌘ + Z |
The board is a single Tab stop; arrow keys move inside it. If the game pauses, focus moves to Resume and comes back to the same cell afterwards.
With Highlight rule breaks on (the default), cells that break a rule get a soft red tint: three in a row, more than three of a symbol in a line, or a broken = / × sign. It only checks the rules mechanically and never tells you whether a cell matches the solution. Turn it off under the board for a pure challenge.
Hints (3 per puzzle) first check your board for mistakes, which is free. Then they teach the next step: the technique’s name, why it applies, the cells it rests on outlined, and the cells it proves filled in. Best times only count puzzles solved without hints.
Solving techniques
Every puzzle here is checked by a solver that uses only these 5 techniques, easiest first. Easy and Medium boards never need Lookahead; Hard boards need it at least twice. Hints and the solver use the same names, and each links back here.
In the examples: the cells ringed purple are what the reasoning rests on, and the cell ringed green is what it proves. “This cell” means the green one.
1. Pairs
Two matching symbols side by side: the cells on either side of them take the other symbol.
Whenever two suns (or two moons) sit side by side in a row or column, the cells on both ends of that pair must be the other symbol. A third matching symbol next to them would make three in a row.
Worked example (Daily #3): Column 5 has two suns side by side, so the cell next to the pair must be a moon. A third sun would make three in a row.
2. Sandwich
Two matching symbols with one gap between them: the gap takes the other symbol.
Two matching symbols with exactly one empty cell between them: the cell in the middle must be the other symbol, or the three would line up.
Worked example (Daily #1): This cell in row 1 sits between two moons, so it must be a sun. Another moon would make three in a row.
3. Balance
A row or column already has its three of one symbol: every other cell takes the other symbol.
Every row and column has exactly three suns and three moons. Once a line has its three of one symbol, every remaining cell in it is the other symbol. Count as you go: this one finishes lines fast.
Worked example (Daily #3): Column 5 already has all three of its suns, so its other cells must all be moons.
4. Link
An = or × sign with one side filled tells you the other side.
An = between two cells means they hold the same symbol; a × means they hold different symbols. As soon as one side of a sign is filled, the other side follows.
Worked example (Daily #11): The × sign means this cell is the opposite of its neighbor at row 5, column 6, which is a moon. So this cell is a sun.
5. Lookahead
Try a symbol in your head: if one more forced move would break a rule, the cell must be the other symbol.
When nothing above applies, try a symbol in a cell in your head and follow it one step. If that one forced move breaks a rule (three in a row, four of a symbol in a line, or a broken = / × sign), your guess was impossible, so the cell is the other symbol.
This is what makes Hard boards hard. Good places to try it: a line that already has two of one symbol, and cells next to a sign.
Worked example (Daily #24): Suppose this cell were a moon: row 1 would have all three of its moons, so its other empty cells would have to be suns, and row 1 would get three suns in a row. So this cell must be a sun.