One answer per square
Sudoku
Use logic to complete every row, column, and three-by-three box with the numbers 1 through 9.
Make every digit fit
Mark a thought.
Prove the answer.
Tap a square, then choose a number. Notes add small candidates instead. On a keyboard, use Arrow keys to move, 1–9 to enter, N for notes, and Backspace to erase. Your unfinished puzzle stays on this device.