3 Write a number in every blank square of the grid. When the grid is
4 full, every orthogonally connected group of identical numbers should
5 have an area equal to that number: so 1s always appear alone, 2s in
8 To place a number, click the mouse in a blank square to select it,
9 then type the number you want on the keyboard. You can also drag to
10 select multiple squares, and then type a number to place it in all
11 of them. To erase numbers, select one or more squares in the same
12 way and then press Backspace.