Challenging Sudoku Logic Puzzles (Vol 1) Step-by-Step Instructions for Puzzle 113   (56/81) Diff: 18/44.322B.1211.2344.7662 The numbers in the puzzle below refer to the step number at which the value of the location can be deduced. Locations without step numbers contain the initial values found in corresponding puzzle in your edition of the book.

Rows are numbered top to bottom, columns from left to right, and rectangles from left to right and then top to bottom. Coordinates are (col, row). Precise details on numbering within each group are specified in the on-line instructions for 'Sudoku' puzzles.

Step 1. There are 4 independent moves.

• The only spot left for 1 in the 1st row is at (6, 1).
• The only spot left for 3 in the 1st 3x3 square is at (1, 2).
• The only spot left for 1 in the 3rd 3x3 square is at (9, 3).
• The only spot left for 1 in the 4th 3x3 square is at (1, 4).

Step 2. There are 4 independent moves.

• The only spot left for 1 in the 8th row is at (2, 8).
• The only spot left for 4 in the 1st column is at (1, 6).
• The only spot left for 4 in the 1st 3x3 square is at (2, 2).
• The only spot left for 1 in the 8th 3x3 square is at (5, 9).

Step 3. There are 3 independent moves.

• The only spot left for 2 in the 8th row is at (6, 8).
• The only spot left for 5 in the 1st column is at (1, 1).
• The only spot left for 2 in the 7th 3x3 square is at (2, 7).

Step 4. There are 2 independent moves.

• The only spot left for 7 in the 1st column is at (1, 7).
• The only spot left for 9 in the 1st 3x3 square is at (3, 1).

Step 5. There are 2 independent moves.

• The only spot left for 7 in the 1st 3x3 square is at (2, 1).
• The only spot left for 9 in the 7th 3x3 square is at (1, 8).

Step 6. There are 2 independent moves.

• 3 must be placed at (3, 7) because it is the only value left that is not already in the 7th row, the 3rd column or the 7th 3x3 square.
• 4 must be placed at (5, 5) because it is the only value left that is not already in the 5th row, the 5th column or the 5th 3x3 square.

Step 7. There is 1 independent move.

• The only spot left for 3 in the 9th column is at (9, 8).

Step 8. There are 2 independent moves.

• The only spot left for 6 in the 8th row is at (7, 8).
• The only spot left for 6 in the 9th column is at (9, 6).

Step 9. There is 1 independent move.

• The only spot left for 8 in the 8th row is at (8, 8).

Step 10. There is 1 independent move.

• The only spot left for 8 in the 9th column is at (9, 2).

Step 11. There are 2 independent moves.

• The only spot left for 9 in the 9th column is at (9, 7).
• The only spot left for 8 in the 2nd 3x3 square is at (4, 1).

Step 12. There are 3 independent moves.

• The only spot left for 2 in the 1st row is at (7, 1).
• The only spot left for 9 in the 8th 3x3 square is at (4, 9).
• The only spot left for 8 in the 8th 3x3 square is at (6, 7).

Step 13. There are 4 independent moves.

• The only spot left for 4 in the 7th row is at (4, 7).
• The only spot left for 3 in the 4th column is at (4, 4).
• The only spot left for 2 in the 6th 3x3 square is at (8, 4).
• The only spot left for 3 in the 8th 3x3 square is at (6, 9).

Step 14. There are 4 independent moves.

• The only spot left for 6 in the 4th column is at (4, 2).
• The only spot left for 4 in the 8th column is at (8, 9).
• The only spot left for 4 in the 2nd 3x3 square is at (6, 3).
• The only spot left for 4 in the 6th 3x3 square is at (7, 4).

Step 15. There are 7 independent moves.

• The only spot left for 8 in the 4th row is at (5, 4).
• The only spot left for 2 in the 4th column is at (4, 6).
• The only spot left for 5 in the 6th column is at (6, 5).
• The only spot left for 5 in the 2nd 3x3 square is at (4, 3).
• The only spot left for 2 in the 2nd 3x3 square is at (5, 2).
• The only spot left for 8 in the 6th 3x3 square is at (7, 6).
• The only spot left for 7 in the 9th 3x3 square is at (7, 9).

Step 16. There are 6 independent moves.

• The only spot left for 9 in the 2nd row is at (8, 2).
• The only spot left for 6 in the 5th row is at (2, 5).
• The only spot left for 5 in the 2nd column is at (2, 9).
• The only spot left for 9 in the 2nd 3x3 square is at (5, 3).
• The only spot left for 5 in the 4th 3x3 square is at (3, 6).
• The only spot left for 6 in the 5th 3x3 square is at (6, 4).

Step 17. There are 6 independent moves.

• The only spot left for 7 in the 2nd 3x3 square is at (6, 2).
• The only spot left for 7 in the 3rd 3x3 square is at (8, 3).
• The only spot left for 7 in the 4th 3x3 square is at (3, 4).
• The only spot left for 7 in the 5th 3x3 square is at (5, 6).
• The only spot left for 9 in the 6th 3x3 square is at (7, 5).
• The only spot left for 6 in the 7th 3x3 square is at (3, 9).

Step 18. There are 2 independent moves.

• The only spot left for 3 in the 3rd 3x3 square is at (7, 3).
• The only spot left for 3 in the 6th 3x3 square is at (8, 5).