Hard sudoku 2

A hard nine by nine. Somewhere in this grid there is a step that scanning will not find: a pair locked into one line, or four cells sitting at the corners of a rectangle. Everything before and after it is ordinary work, and there is still exactly one answer.

462291845173854749555972519
Show the answer key
462185937375269148891374625956421783238657491714938256143596872589712364627843519

What is on this sheet

Given numbers
27
Difficulty
Hard
Hardest step needed
Y-wing
Grid
9 × 9

About this puzzle

Hard means 25 to 29 given numbers and at least one advanced step — an X-wing, a Y-wing, a box-line reduction. The level is measured by solving, not declared: the generator throws away any grid that its solver can only finish by guessing. The answer key is on the second page.

This particular grid starts with 27 of the 81 numbers already printed, and the hardest technique it asks for is: Y-wing.

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