Slitherlink (also known as "Fences", "Loop the Loop", "Dotty Dilemma", "Sli-Lin", "Great Wall of China") is a logic puzzle. It was invented by Nikoli Puzzles in Japan.
Slitherlink is played on a rectangular lattice of dots. Some of the squares formed by the dots have numbers inside them. The objective is to connect horizontally and vertically adjacent dots so that the lines form a single loop with no loose ends. In addition, the number inside a square represents how many of its four sides are segments in the loop.
Cross+A can solve puzzles from
In Sheep and Wolves the diagram contains the black circles ("sheep") and the black crosses ("wolves"). All sheep are supposed to be contained within the loop, while all the wolves should be kept outside.