Yajilin rules copied from Grandmaster Puzzles:
Blacken some white cells and then draw a single closed loop (without intersections or crossings) through all remaining white cells. Blackened cells cannot share an edge with each other. Some cells are outlined and in gray and cannot be part of the loop. Numbered arrows in such cells indicate the total number of blackened cells that exist in that direction in the grid.
Additionally, each digit has been replaced with a different letter, and you need to figure out which digit each letter represents.