Fill in the grid with digits from 1 to 8 putting one digit per a cell. Each row and column should contain every digit exactly once. If two consecutive digits appear in two neighboring cells, they are separated by a white dot. If the digit in a cell is half of the digit in the neighboring cell, then they are marked by a black dot. The dot between 1 and 2 can either be white or be black.
Grid control: Click at a cell reveals the value chooser. Click at the selected value changes the state of the cell. More details about grid control are at the help page.