Nurikabe is a binary determination puzzle. The challenge is to paint each cell black or white, subject to the following rules: Each numbered cell is a wall cell, the number in it is the number of cells in that wall. Each wall must contain exactly one numbered cell. There must be only one stream, which is not allowed to contain "pools", i.e. 2x2 areas of black cells. The app has manual which teach how to solve the puzzle. Please challenge it.