Sudoku

Fill every empty square so that each row, each column and each outlined 3 by 3 box holds the digits 1 to 9 exactly once. The bold digits on tinted squares are the clues you start with; they cannot be changed.

Pick a square, then press a number on the pad or type it. Backspace, Delete or 0 clears the square. Turn Pencil on to write small candidate digits into a square instead of an answer; entering a real digit wipes that square's pencil marks.

The row, column and box of the selected square are shaded, because those are the three constraints acting on it. A digit that repeats inside one of them turns red and gains a bar underneath, and the status line above counts how many digits clash.

Keyboard: arrow keys move, Home and End jump to the start and end of the row, 1 to 9 enter a digit, 0 or Backspace clears, and P switches the pencil on and off. Every puzzle here has exactly one solution, so you never have to guess.