LITS, formerly known as Nuruomino (ヌルオミノ), is a binary determination puzzle published by Nikoli

Nikoli

Nikoli Co., Ltd. is a Japanese publisher that specializes in games and, especially, logic puzzles. Nikoli is also the nickname of a quarterly magazine issued by the company...

.

Rules

LITS is played on a rectangular grid

Regular grid

A regular grid is a tessellation of n-dimensional Euclidean space by congruent parallelotopes . Grids of this type appear on graph paper and may be used in finite element analysis as well as finite volume methods and finite difference methods...

, typically 10×10; the grid is divided into polyomino

Polyomino

A polyomino is a plane geometric figure formed by joining one or more equal squares edge to edge. It is a polyform whose cells are squares. It may be regarded as a finite subset of the regular square tiling with a connected interior....

es, none of which have fewer than four cells. The goal is to shade in a tetromino

Tetromino

A tetromino is a geometric shape composed of four squares, connected orthogonally. This, like dominoes and pentominoes, is a particular type of polyomino...

 within each pre-printed polyomino in such a way that no two matching tetrominoes are orthogonally adjacent (with rotations and reflections counting as matching), and that the shaded cells form a valid nurikabe

Nurikabe

Nurikabe is a binary determination puzzle named for an invisible wall in Japanese folklore that blocks roads and delays foot travel...

: they are all orthogonally contiguous (form a single polyomino) and contain no 2×2 square tetrominoes as subsets.

History

The puzzle was first printed in Puzzle Communication Nikoli #106; the original title is a combination of 'nuru' (Japanese

Japanese language

is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...

: "to paint") and 'omino' (polyomino

Polyomino

A polyomino is a plane geometric figure formed by joining one or more equal squares edge to edge. It is a polyform whose cells are squares. It may be regarded as a finite subset of the regular square tiling with a connected interior....

). In issue #112, the title was changed to the present one, which represents the four (of five) tetrominoes used in the puzzle: the L-shape, the straight, the T-shape, and the skew (square tetrominoes may never appear in the puzzle as they are a direct violation of the rule).