Link pairs of identical numbers so that each number represents the number of cells along the link, including the cells with the numbers. Cells containing 1 represent paths that are 1-cell long. Paths must follow horizontal or vertical directions and are not allowed to cross or overlap other paths.
History of the puzzle
According to Conceptis Ltd, the puzzle was invented by one editor of Byakuya Shobo publishing company.  When did this happen is uncertain, but probably in the late 1990s on お絵かきパズルランド (Oekaki Puzzle Land) magazine, first published in 1995.
Most commonly this puzzle is known as Link-a-Pix (a name by Conceptis), but the name of this article is based on original name given by Byakuya Shobo, ナンバーネットロジック (Number Net Logic).