Form a single closed loop out of the grid edges, in such a way that every numbered square has exactly that many of its edges included in the loop.
Click on a grid edge to mark it as part of the loop (black), and again to return to marking it as undecided (yellow). Right-click on a grid edge to mark it as definitely not part of the loop (faint grey), and again to mark it as undecided again.
When you have mastered the square grid, look in the Type menu for many other types of tiling!
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