LITS

Description
LITS is binary determination puzzle in which the cells in a grid are split into either shaded or unshaded.

Rules
The objective is shade four connected cells in each shape, subject to the following rules:
 * 1) No two of the same tetrominos, including rotations / reflections are allowed to touch.
 * 2) All shaded cells must connect horizontally or vertically upon completion.
 * 3) No 2x2 area of shaded cells is allowed.

Example
A standard 10x10 LITS and its solution.



Variants
Unless otherwise indicated, standard LITS rules apply to all variants.

LITSO: A 2x2 area of shaded cell is allowed as is the O tetromino.

LITS Twin: Two tetrominos appear in each shape, however must be kept seperate.

Barrier LITS: Some shapes include barriers between cells, tetrominos are not allowed to appear on both sides of the barrier.

LITS Quad: Four tetrominoes, one of each of L, I, T and S appear in each shape, however must be kept separate.

LITS+: Some shapes may remain empty, however no 2x2 area of white cells is allowed.

LITS Inversed: Each shape contains an unshaded tetromino. All shaded cells are connected and there is no 2x2 area of shaded cells.