The full reasoning can be found below the Sudoku.
Apr 24 - Hard
Puzzle Copyright © Kevin Stone
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Reasoning
R2C1 is the only square in row 2 that can be <2>
R6C3 is the only square in row 6 that can be <7>
R8C7 is the only square in row 8 that can be <2>
R8C3 is the only square in row 8 that can be <6>
R9C1 is the only square in row 9 that can be <9>
R7C3 is the only square in column 3 that can be <5>
R4C7 is the only square in column 7 that can be <5>
Intersection of row 2 with block 3. The values <167> only appears in one or more of squares R2C7, R2C8 and R2C9 of row 2. These squares are the ones that intersect with block 3. Thus, the other (non-intersecting) squares of block 3 cannot contain these values.
R1C9 - removing <7> from <3478> leaving <348>
R3C9 - removing <17> from <13478> leaving <348>
Squares R1C9, R3C9 and R7C9 in column 9 form a simple naked triplet. These 3 squares all contain the 3 possibilities <348>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the column.
R2C9 - removing <34> from <13467> leaving <167>
R5C9 - removing <4> from <146> leaving <16>
R8C9 - removing <38> from <3578> leaving <57>
R9C9 - removing <38> from <3578> leaving <57>
Squares R8C9 and R9C9 in column 9 form a simple naked pair. These 2 squares both contain the 2 possibilities <57>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the column.
R2C9 - removing <7> from <167> leaving <16>
R2C8 is the only square in row 2 that can be <7>
R8C8 can only be <3>
R2C9 is the only square in row 2 that can be <1>
R5C9 can only be <6>
R2C7 is the only square in row 2 that can be <6>
R8C9 is the only square in row 8 that can be <7>
R9C9 can only be <5>
R8C5 is the only square in row 8 that can be <5>
R5C4 is the only square in row 5 that can be <5>
R5C5 is the only square in row 5 that can be <9>
R2C2 is the only square in column 2 that can be <3>
R2C5 can only be <4>
R2C3 can only be <9>
R1C5 can only be <3>
R9C5 can only be <8>
R3C4 is the only square in row 3 that can be <9>
R3C6 is the only square in row 3 that can be <1>
R5C6 can only be <4>
R5C1 can only be <1>
R8C1 can only be <8>
R6C2 can only be <8>
R4C2 can only be <9>
R8C2 can only be <1>
R4C3 can only be <4>
R7C1 can only be <3>
R4C8 can only be <1>
R3C3 can only be <8>
R4C4 can only be <3>
R6C8 can only be <4>
R6C7 can only be <3>
R4C6 can only be <8>
R9C4 can only be <7>
R6C6 can only be <6>
R6C4 can only be <1>
R7C6 can only be <2>
R3C7 can only be <4>
R7C4 can only be <6>
R1C6 can only be <7>
R9C6 can only be <3>
R1C4 can only be <2>
R1C1 can only be <4>
R3C1 can only be <7>
R3C9 can only be <3>
R7C7 can only be <8>
R1C9 can only be <8>
R7C9 can only be <4>
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