Slitherlink by Nikoli

"Slitherlink" is a puzzle in which you connect dots with a line according to the rules. The greatest attraction is the fact that there exist an unlimited number of set sequences known as "theorems". With this puzzle, you can actually feel your own skill level rising with each theorem you learn. To ensure your long-term enjoyment, we're prepared both a "Stage Clear" mode and a "Random" mode. In "Stage Clear" mode, you progress by clearing puzzles one by one, and in "Random" mode puzzles are generated at random.