# Orientation Division

The English name of this puzzle type is given by EctoPlasma, the author of the article, who thought that the exact translation of the original Japanese name would be too long and inappropriate. This article covers two separate, but very similar puzzle types, both by Naoki Inaba (Japan).

## Rules

### Domino version

Divide the grid along the given lines into dominoes. Each domino is formed by two orthogonally adjacent cells.

When there is a cross between two dominoes, they must have a different orientation. When there is a dot between two dominoes, they must have the same orientation. Symbols cannot lie inside of a domino.

(Rules and example from WPC 2016 IB)

### Triomino version

Divide the grid along the given lines into triominoes. Each triomino is formed by three orthogonally adjacent cells.

When there is a cross between two triominoes, they must be of a different shape. When there is a triangle between two triominoes, they must be of the same shape, but different orientation. When there is a dot between two triominoes, they must be of the same shape and the same orientation. Symbols cannot lie inside of a triomino.

(Rules and example from WPC 2016 IB)

## History of the puzzle

As said earlier, both versions were invented by Naoki Inaba. Domino version was invented in 2010 under the name タテヨコ分割 (lit. "Vertical-Horizontal Division"),[1] triomino version in 2014 under the name ○△×分割 ("○△× Division").[2]

The name "Orientation Division" is originally given in 2021, since "Vertical-Horizontal Division" is obviously too long, but the name given to a puzzle in WPC 2016 ("Domino/Trimino Divide") is not really a good representation of the rule.