Notes on this puzzle
28 digits are printed in this grid and the other 53 cells are yours to fill. A solver that never guesses gets through it in 60 steps.
Most cells fall to the hidden single move: 52 of the 60 steps. XY-Wing accounts for 2 more. The toughest moment needs X-Wing, and that single step is what sets the level.
Among the givens, 6 is the most common digit (6 times) and 1 the rarest (1). The emptiest box is the top-right one, with 2 givens; the middle-left box is the most crowded, with 5.
Where to beginLook at row 3, column 9 first: a hidden single is available there from the very start. Expect a stage where only a pattern across several lines moves the grid on; full notes make it visible.