Region Coloring
Shading every cell as inside or outside the loop (with the space beyond the grid always outside): a line always separates two different shades, a blank always keeps the same shade. Chaining that logic across the board pins down edges too far apart for any single clue to reach alone.
How it works
- 1The loop splits the board into exactly two regions, inside and outside, with everything beyond the grid counting as outside. A blank edge joins two cells into the same region; a drawn one puts them in different regions.
- 2Start at the top: that cell's own border edge is blank, so it belongs with the outside. The drawn edge below it flips the colour, and the blank edge to the left carries that second colour along.
- 3The bottom-left cell has two blank border edges of its own, so it is outside as well — the first colour again.
- 4Two cells now sit in different regions with the edge between them still undecided, and the rule runs backwards just as well as forwards: different colours means a line. Draw it.
- Edge on the loop
- Edge the technique adds
- Edge ruled out
- Inside / outside the loop