A logic puzzle of arrows and one long loop. Numbered clue cells point along a row or column and say how many shaded cells lie that way. Shade cells so every clue is right, without two shaded cells ever touching side by side, then draw a single closed loop through every remaining white cell. Each board has exactly one solution that pure logic reaches, and a timed run grows from 6×6 to 9×9.
Tap a cell to shade it ■; tap it again for a small dot • (a reminder that the loop passes there), and once more to empty it. Drag from cell to cell to draw the loop; a drag that starts on a loop segment erases instead, and tapping a cell that holds loop segments clears them. Undo takes back your last move and Clear wipes the board.
The grey cells are clues. The number says how many shaded cells lie on the straight line from the clue, in the direction of its arrow, all the way to the edge of the board. Clue cells are never shaded and the loop never enters them. Two shaded cells may touch at a corner but never along a side. Every cell that is neither a clue nor shaded must be visited by one single closed loop that joins the centres of neighbouring cells, never branches and never crosses itself. A clue turns green once its count is right and every cell along its arrow is shaded, dotted or on the loop, and red when there are too many shaded cells along its arrow; two shaded cells that touch get a red outline.
Practice 5×5 is a short coached board with no clock. A run starts with three 6×6 puzzles, then three at 7×7 and three at 8×8, and every puzzle from the 10th on is 9×9. Each puzzle has its own clock: 100, 140, 180 or 220 seconds by size, minus 6 seconds for every puzzle already played in the run, with no lower limit, and it starts when the board appears. When a clock runs out the run is over. Your score is the number of puzzles solved; ties are split by the spare time left on each clock, added up to a tenth of a second. Puzzle 38 would have no time at all, so no run can go past 37 puzzles.
Start with the clues that leave no choice. A 0 rules out shading on its whole line, so every cell it points at is white and carries the loop: mark them with dots. Because shaded cells can never be neighbours, a stretch of three open cells holds at most two of them; when a clue's number equals the most that can fit, the alternating pattern is fixed at once. Clues that point at a nearby edge are usually the quickest.
Then think about the loop. Every white cell needs exactly two loop neighbours, so a white cell in a corner, or one boxed in by clues, shaded cells or the border until only two sides are open, has its path decided. It works the other way round too: if a cell could never get two connections, it must be shaded. And shading a cell forces all four of its side neighbours to be white, which often leaves one of them with only two ways out.
Keep the loop in one piece. If joining two loose ends would close a small ring while white cells are still waiting outside it, that link is wrong. In the same way, a cell whose shading would split the white cells into two separate groups has to stay white, because one loop cannot visit both. These whole-board checks are what usually crack the last stubborn corner.
In a run, speed adds up. Draw long stretches in one drag, put dots on cells you know are white instead of keeping them in your head, and reach for Undo rather than Clear when one step goes wrong. Spare seconds are your tie-break and the clock gets 6 seconds shorter every puzzle, so the early boards are where you bank time.