Slitherlink Puzzle Books - 400 Easy to Master Puzzles 11x11 (Volume 7)

Slitherlink (also known as "Fences", "Loop the Loop", "Dotty Dilemma", "Sli-Lin", "Great Wall of China") is a logic puzzle.

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.