Tap a square to cycle it. An X is your note that a hoop can't go there; it does nothing to the puzzle but keep you straight.
Drag across empty squares to X out a run of them at once. On a mouse, right-click puts a hoop down directly.
Usually one hoop, sometimes two. The chip at the top of the board tells you which.
Each one says how many hoops belong in its line. They show on all four sides, so you can read them from wherever you are looking.
Not side by side, not corner to corner. This is the rule that does most of the work.
Every puzzle has exactly one solution, and it never needs a guess.
Tap a set and look at the board below. The one you like best becomes your default, and you can change it any time under the gear.
No name or email is sent. If you're offline it waits and goes when you're back.
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Tap a square once for an X, twice for a hoop. Drag to X out a run.