How to play
Fill every empty cell so that each row, each column and each 3×3 box contains the digits 1–9 exactly once.
Tap a cell, then tap a number (or use your keyboard). Tap the same number again to clear it. Duplicate digits in a row, column or box are highlighted in red.
The Notes () button cycles through three modes: off, then Maybe to pencil in candidate digits, then Not () to cross out digits you've ruled out. Undo steps back through your moves, all the way to the start.
Keyboard: 1–9 to enter, Backspace to erase, arrows to move, N to cycle notes mode, ⌘/Ctrl+Z to undo.