Hard sudoku 1

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.

9722586995459125391223416473
Show the answer key
549316872321587649687429153734958216968172435152634987815263794293741568476895321

What is on this sheet

Given numbers
28
Difficulty
Hard
Hardest step needed
X-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 28 of the 81 numbers already printed, and the hardest technique it asks for is: X-wing.

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