The full reasoning can be found below the Sudoku.
Mar 02 - Very Hard
Puzzle Copyright © Kevin Stone
Reasoning
R1C6 is the only square in row 1 that can be <7>
R3C5 is the only square in row 3 that can be <1>
R4C6 is the only square in row 4 that can be <1>
R4C2 is the only square in row 4 that can be <2>
R4C5 is the only square in row 4 that can be <8>
R6C2 is the only square in row 6 that can be <7>
R9C7 is the only square in row 9 that can be <7>
R5C9 is the only square in row 5 that can be <7>
R5C3 is the only square in row 5 that can be <5>
R5C1 is the only square in row 5 that can be <8>
R8C5 is the only square in row 8 that can be <7>
R2C1 is the only square in column 1 that can be <6>
R2C3 is the only square in row 2 that can be <2>
R5C7 is the only square in block 6 that can be <3>
R5C5 can only be <6>
R6C8 is the only square in row 6 that can be <6>
R7C9 is the only square in row 7 that can be <6>
R1C7 is the only square in row 1 that can be <6>
R1C9 is the only square in row 1 that can be <1>
R9C4 is the only square in row 9 that can be <6>
R9C6 is the only square in row 9 that can be <3>
R8C7 is the only square in column 7 that can be <1>
R2C9 is the only square in column 9 that can be <3>
R6C5 is the only square in column 5 that can be <3>
R6C4 is the only square in row 6 that can be <4>
Intersection of row 2 with block 2. The values <58> only appears in one or more of squares R2C4, R2C5 and R2C6 of row 2. These squares are the ones that intersect with block 2. Thus, the other (non-intersecting) squares of block 2 cannot contain these values.
R1C4 - removing <8> from <389> leaving <39>
R3C4 - removing <8> from <389> leaving <39>
Squares R1C4 and R3C4 in column 4 form a simple naked pair. These 2 squares both contain the 2 possibilities <39>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the column.
R2C4 - removing <9> from <589> leaving <58>
R5C4 - removing <9> from <29> leaving <2>
R5C6 can only be <9>
R2C7 is the only square in row 2 that can be <9>
R4C7 can only be <4>
Intersection of row 7 with block 8. The value <4> only appears in one or more of squares R7C4, R7C5 and R7C6 of row 7. These squares are the ones that intersect with block 8. Thus, the other (non-intersecting) squares of block 8 cannot contain this value.
R8C6 - removing <4> from <248> leaving <28>
Intersection of row 9 with block 7. The values <18> only appears in one or more of squares R9C1, R9C2 and R9C3 of row 9. These squares are the ones that intersect with block 7. Thus, the other (non-intersecting) squares of block 7 cannot contain these values.
R8C3 - removing <8> from <489> leaving <49>
Squares R1C4, R3C4, R1C2 and R3C2 form a Type-2 Unique Rectangle on <39>.
R1C3 - removing <8> from <489> leaving <49>
R9C2 - removing <8> from <58> leaving <5>
R9C8 can only be <2>
R7C2 can only be <9>
R9C1 can only be <1>
R7C8 can only be <5>
R8C3 can only be <4>
R7C5 can only be <4>
R4C8 can only be <9>
R8C9 can only be <9>
R8C1 can only be <2>
R1C3 can only be <9>
R4C9 can only be <5>
R9C3 can only be <8>
R6C1 can only be <9>
R1C4 can only be <3>
R6C3 can only be <1>
R3C1 can only be <4>
R1C2 can only be <8>
R3C4 can only be <9>
R3C8 can only be <8>
R3C2 can only be <3>
R1C8 can only be <4>
R7C6 can only be <2>
R2C5 can only be <5>
R8C6 can only be <8>
R8C4 can only be <5>
R2C6 can only be <4>
R2C4 can only be <8>
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