     Sudoku Solution Path   Copyright © Kevin Stone R4C5 can only be <5> R6C5 can only be <6> R5C6 can only be <2> R5C4 can only be <8> R9C6 can only be <1> R1C6 can only be <5> R5C5 can only be <7> R1C1 is the only square in row 1 that can be <7> R9C9 is the only square in row 9 that can be <7> R9C8 is the only square in row 9 that can be <4> R5C8 can only be <9> R1C8 can only be <8> Squares R5C7 and R6C9 in block 6 form a simple locked pair. These 2 squares both contain the 2 possibilities <15>. Since each of the squares must contain one of the possibilities, they can be eliminated from the other squares in the block.    R5C9 - removing <15> from <1345> leaving <34> Squares R1C4 and R9C4 in column 4 and R1C7 and R9C7 in column 7 form a Simple X-Wing pattern on possibility <2>. All other instances of this possibility in rows 1 and 9 can be removed.    R9C1 - removing <2> from <25689> leaving <5689>    R1C5 - removing <2> from <1234> leaving <134>    R9C5 - removing <2> from <2389> leaving <389>    R1C9 - removing <2> from <1269> leaving <169> Squares R6C1 and R6C9 in row 6 and R8C1 and R8C9 in row 8 form a Simple X-Wing pattern on possibility <5>. All other instances of this possibility in columns 1 and 9 can be removed.    R5C1 - removing <5> from <13456> leaving <1346>    R9C1 - removing <5> from <5689> leaving <689> Squares R4C1, R4C9, R5C1 and R5C9 form a Type-1 Unique Rectangle on <34>.    R5C1 - removing <34> from <1346> leaving <16> Squares R1C4 (XY), R1C7 (XZ) and R2C5 (YZ) form an XY-Wing pattern on <1>. All squares that are buddies of both the XZ and YZ squares cannot be <1>.    R2C9 - removing <1> from <16> leaving <6>    R1C5 - removing <1> from <134> leaving <34> R2C1 can only be <3> R2C5 can only be <1> R4C1 can only be <4> R4C9 can only be <3> R3C1 can only be <9> R5C9 can only be <4> R3C9 can only be <2> R1C2 can only be <6> R3C5 can only be <4> R7C9 can only be <8> R1C7 can only be <1> R7C1 can only be <2> R8C9 can only be <5> R6C9 can only be <1> R9C7 can only be <2> R9C4 can only be <3> R1C3 can only be <4> R5C2 can only be <3> R9C2 can only be <9> R1C5 can only be <3> R1C4 can only be <2> R1C9 can only be <9> R5C7 can only be <5> R5C3 can only be <6> R6C1 can only be <5> R7C5 can only be <9> R8C1 can only be <8> R9C5 can only be <8> R8C5 can only be <2> R9C1 can only be <6> R9C3 can only be <5> R5C1 can only be <1> [Puzzle Code = Sudoku-20190212-SuperHard-252109]    