Difficult Sudoku Twelve Logic Puzzles (Vol 1) Step-by-Step Instructions for Puzzle 28   (80/144) Diff: 10/85.9978.7991 Printable puzzle or puzzle with instructions 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-12up' puzzles.

Step 1. There are 8 independent moves.

• The only spot left for 6 in the 11th row is at (6, 11).
• The only spot left for 6 in the 9th column is at (9, 12).
• The only spot left for A in the 12th column is at (12, 9).
• The only spot left for 4 in the 2nd 3x4 rectangle is at (6, 4).
• The only spot left for 9 in the 2nd 3x4 rectangle is at (4, 3).
• The only spot left for A in the 7th 3x4 rectangle is at (9, 5).
• The only spot left for 4 in the 8th 3x4 rectangle is at (11, 5).
• The only spot left for B in the 10th 3x4 rectangle is at (5, 10).

Step 2. There are 5 independent moves.

• The only spot left for B in the 5th row is at (12, 5).
• The only spot left for 1 in the 10th row is at (12, 10).
• The only spot left for A in the 2nd 3x4 rectangle is at (4, 1).
• The only spot left for 1 in the 10th 3x4 rectangle is at (5, 9).
• The only spot left for A in the 11th 3x4 rectangle is at (7, 11).

Step 3. There are 12 independent moves.

• The only spot left for A in the 4th row is at (11, 4).
• The only spot left for 9 in the 9th row is at (8, 9).
• The only spot left for 3 in the 11th row is at (11, 11).
• The only spot left for 5 in the 12th column is at (12, 2).
• The only spot left for 8 in the 2nd 3x4 rectangle is at (5, 1).
• The only spot left for A in the 3rd 3x4 rectangle is at (8, 3).
• The only spot left for B in the 4th 3x4 rectangle is at (10, 2).
• The only spot left for 1 in the 8th 3x4 rectangle is at (11, 8).
• The only spot left for 1 in the 9th 3x4 rectangle is at (1, 12).
• The only spot left for 9 in the 10th 3x4 rectangle is at (5, 11).
• The only spot left for 5 in the 12th 3x4 rectangle is at (11, 12).
• The only spot left for 9 in the 12th 3x4 rectangle is at (10, 10).

Step 4. There are 9 independent moves.

• The only spot left for 7 in the 3rd row is at (9, 3).
• The only spot left for 9 in the 7th row is at (12, 7).
• The only spot left for 5 in the 1st column is at (1, 4).
• The only spot left for 3 in the 2nd 3x4 rectangle is at (4, 2).
• The only spot left for 8 in the 4th 3x4 rectangle is at (11, 3).
• The only spot left for 0 in the 4th 3x4 rectangle is at (10, 1).
• The only spot left for 9 in the 7th 3x4 rectangle is at (7, 8).
• The only spot left for 5 in the 11th 3x4 rectangle is at (8, 10).
• The only spot left for 8 in the 12th 3x4 rectangle is at (10, 12).

Step 5. There are 7 independent moves.

• The only spot left for B in the 8th row is at (6, 8).
• The only spot left for 5 in the 3rd column is at (3, 9).
• The only spot left for 0 in the 2nd 3x4 rectangle is at (6, 2).
• The only spot left for B in the 3rd 3x4 rectangle is at (7, 3).
• The only spot left for B in the 7th 3x4 rectangle is at (9, 7).
• The only spot left for 2 in the 8th 3x4 rectangle is at (12, 8).
• The only spot left for 2 in the 11th 3x4 rectangle is at (9, 10).

Step 6. There are 8 independent moves.

• The only spot left for 3 in the 3rd row is at (2, 3).
• The only spot left for 7 in the 8th row is at (8, 8).
• The only spot left for 0 in the 3rd column is at (3, 5).
• The only spot left for 3 in the 9th column is at (9, 6).
• The only spot left for 1 in the 2nd 3x4 rectangle is at (6, 1).
• The only spot left for 3 in the 3rd 3x4 rectangle is at (8, 1).
• The only spot left for 7 in the 6th 3x4 rectangle is at (6, 7).
• The only spot left for 2 in the 7th 3x4 rectangle is at (8, 7).

Step 7. There are 7 independent moves.

• The only spot left for 6 in the 1st row is at (3, 1).
• The only spot left for 3 in the 7th row is at (1, 7).
• The only spot left for 6 in the 3rd 3x4 rectangle is at (8, 2).
• The only spot left for 2 in the 5th 3x4 rectangle is at (1, 5).
• The only spot left for 0 in the 6th 3x4 rectangle is at (5, 6).
• The only spot left for 3 in the 8th 3x4 rectangle is at (10, 8).
• The only spot left for 3 in the 11th 3x4 rectangle is at (7, 12).

Step 8. There are 13 independent moves.

• The only spot left for 1 in the 2nd row is at (3, 2).
• The only spot left for 5 in the 6th row is at (2, 6).
• The only spot left for 6 in the 7th row is at (4, 7).
• The only spot left for 0 in the 12th row is at (4, 12).
• The only spot left for 8 in the 1st column is at (1, 11).
• The only spot left for 7 in the 3rd column is at (3, 11).
• The only spot left for 1 in the 8th column is at (8, 6).
• The only spot left for 7 in the 1st 3x4 rectangle is at (1, 1).
• The only spot left for 1 in the 3rd 3x4 rectangle is at (7, 4).
• The only spot left for 5 in the 6th 3x4 rectangle is at (5, 8).
• The only spot left for 3 in the 6th 3x4 rectangle is at (5, 5).
• The only spot left for 6 in the 8th 3x4 rectangle is at (10, 6).
• The only spot left for 0 in the 11th 3x4 rectangle is at (7, 10).

Step 9. There are 10 independent moves.

• The only spot left for 8 in the 7th row is at (3, 7).
• The only spot left for 4 in the 10th row is at (2, 10).
• The only spot left for 2 in the 3rd column is at (3, 4).
• The only spot left for 6 in the 5th 3x4 rectangle is at (2, 8).
• The only spot left for 8 in the 6th 3x4 rectangle is at (4, 8).
• The only spot left for 4 in the 7th 3x4 rectangle is at (7, 6).
• The only spot left for 2 in the 9th 3x4 rectangle is at (2, 11).
• The only spot left for 0 in the 9th 3x4 rectangle is at (2, 9).
• The only spot left for 4 in the 10th 3x4 rectangle is at (4, 9).
• The only spot left for 4 in the 11th 3x4 rectangle is at (8, 12).

Step 10. There is 1 independent move.

• The only spot left for 8 in the 1st 3x4 rectangle is at (2, 4).