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Feb 27 - Super Hard

## Reasoning

R1C4 can only be <6>

R4C4 can only be <2>

R4C6 can only be <1>

R6C4 can only be <7>

R9C4 can only be <3>

R4C1 can only be <3>

R4C9 can only be <6>

R1C8 is the only square in row 1 that can be <3>

R1C3 is the only square in row 1 that can be <5>

R1C7 is the only square in row 1 that can be <1>

R1C2 is the only square in row 1 that can be <7>

R5C2 can only be <8>

R5C5 can only be <9>

R6C1 can only be <1>

R1C5 can only be <4>

R6C6 can only be <8>

R6C9 can only be <9>

R5C1 can only be <7>

R9C6 can only be <4>

R1C6 can only be <9>

R8C5 can only be <8>

R2C5 can only be <2>

R9C5 can only be <1>

R2C9 is the only square in row 2 that can be <5>

R3C3 is the only square in row 3 that can be <1>

R3C8 is the only square in row 3 that can be <7>

R8C3 is the only square in row 8 that can be <7>

R8C9 is the only square in row 8 that can be <3>

R7C3 is the only square in row 7 that can be <3>

Intersection of column 8 with block 9. The value <9> only appears in one or more of squares R7C8, R8C8 and R9C8 of column 8. These squares are the ones that intersect with block 9. Thus, the other (non-intersecting) squares of block 9 cannot contain this value.

R7C7 - removing <9> from <2489> leaving <248>

R9C7 - removing <9> from <2689> leaving <268>

Squares R7C2<24>, R8C1<46> and R9C2<26> in block 7 form a comprehensive naked triplet. These 3 squares can only contain the 3 possibilities <246>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the block.

R7C1 - removing <4> from <489> leaving <89>

Squares R2C1 and R2C7 in row 2 and R8C1 and R8C7 in row 8 form a Simple X-Wing pattern on possibility <4>. All other instances of this possibility in columns 1 and 7 can be removed.

R3C1 - removing <4> from <469> leaving <69>

R3C7 - removing <4> from <249> leaving <29>

R7C7 - removing <4> from <248> leaving <28>

Squares R5C8, R5C9, R7C8 and R7C9 form a Type-4 Unique Rectangle on <12>.

R7C8 - removing <2> from <129> leaving <19>

R7C9 - removing <2> from <124> leaving <14>

Squares R7C7 (XY), R3C7 (XZ) and R7C1 (YZ) form an XY-Wing pattern on <9>. All squares that are buddies of both the XZ and YZ squares cannot be <9>.

R3C1 - removing <9> from <69> leaving <6>

R3C2 can only be <4>

R8C1 can only be <4>

R3C9 can only be <2>

R7C2 can only be <2>

R3C7 can only be <9>

R5C9 can only be <1>

R5C8 can only be <2>

R7C9 can only be <4>

R7C7 can only be <8>

R9C2 can only be <6>

R7C1 can only be <9>

R8C7 can only be <6>

R9C7 can only be <2>

R9C8 can only be <9>

R9C3 can only be <8>

R7C8 can only be <1>

R2C7 can only be <4>

R2C1 can only be <8>

R2C3 can only be <9>

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