     Sudoku Solution Path   Copyright © Kevin Stone R2C9 can only be <1> R6C6 can only be <5> R4C6 can only be <9> R2C6 can only be <4> R8C6 can only be <8> R5C5 is the only square in row 5 that can be <8> R5C2 is the only square in row 5 that can be <9> R8C5 is the only square in row 8 that can be <6> R6C2 is the only square in column 2 that can be <4> Squares R5C3 and R5C7 in row 5 form a simple locked pair. These 2 squares both contain the 2 possibilities <13>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the row.    R5C1 - removing <3> from <35> leaving <5>    R5C8 - removing <13> from <12345> leaving <245> R4C8 is the only square in row 4 that can be <5> Squares R4C4 and R6C4 in column 4 form a simple locked pair. These 2 squares both contain the 2 possibilities <13>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the column.    R2C4 - removing <3> from <359> leaving <59>    R8C4 - removing <1> from <159> leaving <59> Squares R2C3<37>, R2C4<59>, R2C5<3579> and R2C7<39> in row 2 form a comprehensive locked quad. These 4 squares can only contain the 4 possibilities <3579>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the row.    R2C1 - removing <3> from <23> leaving <2>    R2C2 - removing <37> from <23678> leaving <268>    R2C8 - removing <39> from <3689> leaving <68> R8C1 can only be <3> Squares R7C2 and R8C3 in block 7 form a simple locked pair. These 2 squares both contain the 2 possibilities <17>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the block.    R8C2 - removing <17> from <1257> leaving <25>    R9C2 - removing <1> from <125> leaving <25> Squares R5C3 and R8C3 in column 3 and R5C7 and R8C7 in column 7 form a Simple X-Wing pattern on possibility <1>. All other instances of this possibility in rows 5 and 8 can be removed.    R8C8 - removing <1> from <12479> leaving <2479> Squares R2C3 and R5C3 in column 3 and R2C7 and R5C7 in column 7 form a Simple X-Wing pattern on possibility <3>. All other instances of this possibility in rows 2 and 5 can be removed.    R2C5 - removing <3> from <3579> leaving <579> Squares R3C5 and R3C8 in row 3 and R7C5 and R7C8 in row 7 form a Simple X-Wing pattern on possibility <9>. All other instances of this possibility in columns 5 and 8 can be removed.    R2C5 - removing <9> from <579> leaving <57>    R8C8 - removing <9> from <2479> leaving <247> Squares R5C8, R5C9, R8C8 and R8C9 form a Type-1 Unique Rectangle on <24>.    R8C8 - removing <24> from <247> leaving <7> R8C3 can only be <1> R8C7 can only be <9> R5C3 can only be <3> R7C2 can only be <7> R8C4 can only be <5> R2C7 can only be <3> R7C8 can only be <1> R2C3 can only be <7> R5C7 can only be <1> R1C8 can only be <6> R4C2 can only be <1> R6C8 can only be <3> R6C4 can only be <1> R7C5 can only be <9> R9C8 can only be <2> R8C2 can only be <2> R2C4 can only be <9> R9C5 can only be <1> R9C2 can only be <5> R5C8 can only be <4> R8C9 can only be <4> R1C2 can only be <3> R2C8 can only be <8> R2C5 can only be <5> R3C5 can only be <3> R2C2 can only be <6> R3C8 can only be <9> R3C2 can only be <8> R1C5 can only be <7> R4C4 can only be <3> R5C9 can only be <2> [Puzzle Code = Sudoku-20190712-VeryHard-247763]    