Notes on this puzzle
26 digits are printed in this grid and the other 55 cells are yours to fill. A solver that never guesses gets through it in 56 steps.
Most cells fall to the hidden single move: 54 of the 56 steps. Single candidate accounts for 1 more. The toughest moment needs pointing pair, and that single step is what sets the level.
Among the givens, 7 is the most common digit (5 times) and 2 the rarest (2). The emptiest box is the top-left one, with 1 given; the top-right box is the most crowded, with 4.
Where to beginLook at row 2, column 6 first: a hidden single is available there from the very start. Pencil in candidates for one box at a time and watch for two cells that share the same pair.