01
Pencil marks
Why B1 allows 2 and 8—and why neither is an answer yet.
SMART SUDOKU
Learn Sudoku, one reason at a time.
Start with candidates, then turn a possibility into a move you can explain. Each lesson uses a real starter board and checks the row, column and box.
02
Naked single
Follow the row, column and box to see why A7 must be 7.
Ready for an X-Wing?
Follow both possible placements and see why other candidates can be removed.
View the worked X-Wing ↗