Tetroid is a logic puzzle invented by Naoki Inaba (Japan). A rectangular or square grid contains black cells. The aim is to divide the grid into regions of exactly four cells, to form an L, I, T, S or O tetromino.Black cells do not belong to any tetromino. The tetrominoes may be rotated or mirrored. When two tetrominoes in adjacent regions share an edge, they must not be of the same type. puzzle games for adults - puzzle game for adults - puzzle game book - puzzle game adult - puzzle game brain teaser - puzzle game gift - jigsaw puzzle games - logic game book - logic game puzzles - logic games for adults - math games - math game adult - math game books - brain games - brain games for adults - brain game books - brain game puzzles - brain game adults - brain game books for seniors - brain game for adult - brain game large print