Tetoron is a logic puzzle invented by Nishiyama Yukari (Japan). A rectangular or square grid contains symbols in some cells. The goal is to divide the grid into regions of exactly four cells (tetromino). Each region contains exactly two different symbols. Regions of the same shape must contain the same symbols. The tetrominoes may be rotated or mirrored.
Cross+A can solve puzzles from 3 x 3 to 30 x 30.