Shade some cells of the grid to create a number of triominoes. A trimino is a triplet of cells that are interconnected by their edges. No two triominoes can share an edge but they can touch each other by corners. Each of the given circles must be a part of a trimino.
(Rules and example from WPC 2016 IB)
History of the puzzle
The name of this article is based on the name given by Naoki Inaba (Japan) in 2010 when he first published this puzzle type on his website.  However, due to the simplicity of the rules, it is possible that the same ruleset has been proposed elsewhere independently.
Appearances in the past WPCs
- WPC 2016/Round 8 by Matúš Demiger