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Nov 29 - Super Hard

## Reasoning

R1C4 can only be <1>

R3C8 can only be <1>

R5C5 can only be <2>

R2C4 can only be <2>

R3C2 can only be <2>

R6C2 can only be <5>

R6C1 can only be <2>

R6C8 can only be <4>

R6C9 can only be <1>

R2C8 is the only square in row 2 that can be <5>

Squares R7C8<67>, R8C7<79> and R9C9<679> in block 9 form a comprehensive naked triplet. These 3 squares can only contain the 3 possibilities <679>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the block.

R8C8 - removing <679> from <236789> leaving <238>

R8C9 - removing <679> from <2679> leaving <2>

R9C8 - removing <679> from <36789> leaving <38>

R4C8 is the only square in row 4 that can be <2>

Squares R4C2<379>, R5C2<79>, R7C2<67> and R9C2<367> in column 2 form a comprehensive naked quad. These 4 squares can only contain the 4 possibilities <3679>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the column.

R1C2 - removing <36> from <3468> leaving <48>

R2C2 - removing <36> from <13468> leaving <148>

R8C2 - removing <367> from <13467> leaving <14>

Intersection of column 2 with block 7. The value <6> only appears in one or more of squares R7C2, R8C2 and R9C2 of column 2. These squares are the ones that intersect with block 7. Thus, the other (non-intersecting) squares of block 7 cannot contain this value.

R8C1 - removing <6> from <34567> leaving <3457>

R9C1 - removing <6> from <3567> leaving <357>

R8C4 is the only square in row 8 that can be <6>

R9C4 can only be <7>

Squares R5C2 and R5C8 in row 5 and R7C2 and R7C8 in row 7 form a Simple X-Wing pattern on possibility <7>. All other instances of this possibility in columns 2 and 8 can be removed.

R4C2 - removing <7> from <379> leaving <39>

Squares R2C5 and R8C5 in column 5 and R2C7 and R8C7 in column 7 form a Simple X-Wing pattern on possibility <9>. All other instances of this possibility in rows 2 and 8 can be removed.

R2C6 - removing <9> from <389> leaving <38>

R8C6 - removing <9> from <589> leaving <58>

R2C9 - removing <9> from <4679> leaving <467>

Squares R1C8 (XY), R7C8 (XZ) and R2C7 (YZ) form an XY-Wing pattern on <7>. All squares that are buddies of both the XZ and YZ squares cannot be <7>.

R8C7 - removing <7> from <79> leaving <9>

R8C5 can only be <8>

R2C7 can only be <7>

R9C9 can only be <6>

R9C2 can only be <3>

R7C8 can only be <7>

R2C9 can only be <4>

R1C9 can only be <9>

R7C2 can only be <6>

R5C8 can only be <9>

R8C6 can only be <5>

R8C8 can only be <3>

R2C5 can only be <9>

R9C6 can only be <9>

R8C3 can only be <1>

R9C8 can only be <8>

R9C1 can only be <5>

R4C2 can only be <9>

R1C8 can only be <6>

R4C9 can only be <7>

R5C2 can only be <7>

R4C1 can only be <3>

R8C2 can only be <4>

R2C3 can only be <3>

R2C1 can only be <6>

R2C6 can only be <8>

R1C1 can only be <4>

R2C2 can only be <1>

R1C6 can only be <3>

R8C1 can only be <7>

R1C2 can only be <8>

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