Nov 14 - Super Hard
Puzzle Copyright © Kevin Stone
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Reasoning
R4C4 can only be <4>
R6C4 can only be <9>
R8C6 can only be <9>
R5C5 can only be <7>
R2C4 can only be <7>
R8C4 can only be <1>
R2C6 can only be <2>
R3C2 is the only square in row 3 that can be <7>
R6C8 is the only square in row 6 that can be <1>
R7C7 is the only square in row 7 that can be <1>
R2C9 is the only square in row 2 that can be <1>
R7C2 is the only square in row 7 that can be <9>
R9C1 can only be <1>
R8C8 is the only square in row 8 that can be <7>
R9C9 is the only square in row 9 that can be <9>
R8C9 is the only square in column 9 that can be <3>
Intersection of row 8 with block 7. The values <48> only appears in one or more of squares R8C1, R8C2 and R8C3 of row 8. These squares are the ones that intersect with block 7. Thus, the other (non-intersecting) squares of block 7 cannot contain these values.
R7C3 - removing <8> from <238> leaving <23>
R9C2 - removing <8> from <368> leaving <36>
Squares R5C3 and R8C3 in column 3 and R5C7 and R8C7 in column 7 form a Simple X-Wing pattern on possibility <6>. All other instances of this possibility in rows 5 and 8 can be removed.
R8C2 - removing <6> from <2468> leaving <248>
R5C9 - removing <6> from <26> leaving <2>
R1C9 can only be <6>
R4C2 is the only square in row 4 that can be <2>
Squares R6C2 (XY), R1C2 (XZ) and R5C3 (YZ) form an XY-Wing pattern on <4>. All squares that are buddies of both the XZ and YZ squares cannot be <4>.
R2C3 - removing <4> from <348> leaving <38>
R3C3 - removing <4> from <234> leaving <23>
Squares R3C3 and R7C3 in column 3 form a simple naked pair. These 2 squares both contain the 2 possibilities <23>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the column.
R2C3 - removing <3> from <38> leaving <8>
R8C3 - removing <2> from <2468> leaving <468>
R8C2 is the only square in row 8 that can be <8>
Intersection of column 2 with block 1. The value <4> only appears in one or more of squares R1C2, R2C2 and R3C2 of column 2. These squares are the ones that intersect with block 1. Thus, the other (non-intersecting) squares of block 1 cannot contain this value.
R1C1 - removing <4> from <2459> leaving <259>
R2C1 - removing <4> from <459> leaving <59>
Squares R2C1 and R2C7 in row 2 form a simple naked pair. These 2 squares both contain the 2 possibilities <59>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the row.
R2C2 - removing <5> from <345> leaving <34>
R2C8 - removing <5> from <345> leaving <34>
Squares R2C1 and R2C7 in row 2 and R5C1 and R5C7 in row 5 form a Simple X-Wing pattern on possibility <5>. All other instances of this possibility in columns 1 and 7 can be removed.
R1C1 - removing <5> from <259> leaving <29>
Squares R1C2 (XY), R1C5 (XZ) and R2C1 (YZ) form an XY-Wing pattern on <9>. All squares that are buddies of both the XZ and YZ squares cannot be <9>.
R1C1 - removing <9> from <29> leaving <2>
R8C1 can only be <4>
R3C3 can only be <3>
R7C3 can only be <2>
R2C2 can only be <4>
R7C8 can only be <8>
R7C5 can only be <3>
R9C8 can only be <6>
R8C3 can only be <6>
R5C1 can only be <5>
R8C7 can only be <2>
R5C3 can only be <4>
R9C2 can only be <3>
R3C7 can only be <9>
R9C5 can only be <8>
R4C8 can only be <5>
R2C8 can only be <3>
R1C2 can only be <5>
R3C5 can only be <4>
R2C7 can only be <5>
R4C6 can only be <6>
R1C8 can only be <4>
R5C7 can only be <6>
R2C1 can only be <9>
R6C2 can only be <6>
R6C6 can only be <5>
R1C5 can only be <9>
R3C8 can only be <2>
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