  In the Nikoli pencil-and-paper game Double Choco, a puzzle consists of an m
$\times$ n grid of cells of white or gray color, separated by dotted lines
where each cell possibly contains an integer. The goal is to partition the grid
into blocks by drawing solid lines over the dotted lines, where every block
must contain a pair of areas of white and gray cells having the same form (size
and shape). An integer indicates the number of cells of that color in the
block. A block can contain any number of cells with the integer. We prove this
puzzle NP-complete, establishing a Nikoli gap of 2 years.
