Shade some cells to make some triominos so that each triomino will be cut twice by thick lines. In each region, exactly three cells are shaded.
(Example from WPC 2015 IB)
History of the puzzle
Invented by Ko Okamoto (Japan). First appeared on an online contest No Numbers, held in May 2012.
Appearances in the past WPCs
- WPC 2015/Round 10 by Vladimir Portugalov