     Sudoku Solution Path   Copyright © Kevin Stone R3C1 can only be <1> R8C3 can only be <3> R2C1 can only be <2> R3C9 is the only square in row 3 that can be <4> R1C4 is the only square in row 1 that can be <4> R3C3 is the only square in row 3 that can be <5> R6C3 is the only square in row 6 that can be <4> R6C5 is the only square in row 6 that can be <5> R8C5 is the only square in row 8 that can be <2> R9C7 is the only square in row 9 that can be <2> R9C1 is the only square in row 9 that can be <4> R9C9 is the only square in row 9 that can be <5> R1C7 is the only square in row 1 that can be <5> R2C4 is the only square in row 2 that can be <5> R4C1 is the only square in column 1 that can be <3> R1C3 is the only square in column 3 that can be <8> R9C6 is the only square in column 6 that can be <6> R9C3 can only be <9> R4C3 can only be <6> R7C9 is the only square in row 7 that can be <9> R6C8 is the only square in row 6 that can be <9> R9C5 is the only square in row 9 that can be <3> R2C7 is the only square in row 2 that can be <3> R1C6 is the only square in row 1 that can be <3> R6C9 is the only square in row 6 that can be <3> Intersection of block 2 with column 5. The value <1> only appears in one or more of squares R1C5, R2C5 and R3C5 of block 2. These squares are the ones that intersect with column 5. Thus, the other (non-intersecting) squares of column 5 cannot contain this value.    R4C5 - removing <1> from <1789> leaving <789> Intersection of block 6 with column 7. The value <1> only appears in one or more of squares R4C7, R5C7 and R6C7 of block 6. These squares are the ones that intersect with column 7. Thus, the other (non-intersecting) squares of column 7 cannot contain this value.    R7C7 - removing <1> from <178> leaving <78> Squares R4C4 and R7C4 in column 4 and R4C7 and R7C7 in column 7 form a Simple X-Wing pattern on possibility <8>. All other instances of this possibility in rows 4 and 7 can be removed.    R4C5 - removing <8> from <789> leaving <79> Squares R4C2 and R4C5 in row 4 form a simple locked pair. These 2 squares both contain the 2 possibilities <79>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the row.    R4C4 - removing <7> from <178> leaving <18>    R4C7 - removing <7> from <178> leaving <18> Intersection of column 4 with block 8. The value <7> only appears in one or more of squares R7C4, R8C4 and R9C4 of column 4. 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 <7> from <178> leaving <18> Squares R1C5 and R1C9 in row 1, R4C2 and R4C5 in row 4 and R8C2 and R8C9 in row 8 form a Swordfish pattern on possibility <7>. All other instances of this possibility in columns 2, 5 and 9 can be removed.    R5C5 - removing <7> from <789> leaving <89>    R5C9 - removing <7> from <78> leaving <8>    R7C2 - removing <7> from <167> leaving <16> R5C5 can only be <9> R4C7 can only be <1> R4C4 can only be <8> R6C7 can only be <7> R5C1 can only be <7> R4C5 can only be <7> R6C6 can only be <1> R7C7 can only be <8> R4C2 can only be <9> R1C5 can only be <1> R7C1 can only be <6> R8C6 can only be <8> R7C2 can only be <1> R1C1 can only be <9> R7C4 can only be <7> R8C2 can only be <7> R9C4 can only be <1> R8C9 can only be <1> R3C6 can only be <7> R1C9 can only be <7> R9C8 can only be <7> R3C8 can only be <8> R1C2 can only be <6> R2C5 can only be <8> R2C8 can only be <1> [Puzzle Code = Sudoku-20180912-VeryHard-040183]    