Normal sudoku rules apply. Fog covers the grid. Correctly placing digits clears the fog. A black dot in a cell indicates its value has a 2-to-1 ratio with that of some neighbor (where "neighbor" means a horizontally or vertically adjacent cell). A white dot in a cell indicates its value is adjacent to the value of some neighbor. A grey dot in a cell indicates that its value and some neighbor's value sum to 5. All possible dots have been given, but some dots may be hiding behind other dots.