3 Fill in the grid with a pattern of black and white squares, so that
4 the numbers in each row and column match the lengths of consecutive
7 Left-click in a square to mark it black; right-click (or hold Ctrl
8 while left-clicking) to mark it white. Click and drag along a row or
9 column to mark multiple squares black or white at once. Middle-click
10 (or hold Shift while left-clicking) to return a square to grey
11 (meaning undecided): dragging like that can erase a whole rectangle,
12 not just a row or column.