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Fill every square with a dot or a ring. Tap a square once for a dot, again for a ring, a third time to clear it. Dark squares are given.
Take this row. Two dots sit side by side, and there are rings further along.
Step 1. A third dot next to the two dots would make three in a row, so the third square must be a ring.
Step 2. The row now has two dots and three rings. It needs three of each, so the last empty square is a dot.
Every square was forced by a rule, so you never need to guess.
Every puzzle has exactly one answer and can be solved by logic alone. Rule breaks turn the squares red as you play. A hint adds 15 seconds. Use the arrow keys and Space if you prefer the keyboard.
Saved on this device.