Variations on Difficult Education Sudoku Logic Puzzles (Vol 1) Step-by-Step Instructions for Puzzle 21   (58/81) Diff: 14/44.3112.3456.5694 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 'HyperEducation' puzzles.

Step 1. There are 4 independent moves.

• The only spot left for E in the 2nd 3x3 square is at (4, 3).
• The only spot left for C in the 1st 3x3 inner square is at (2, 2).
• The only spot left for N in the 2nd 3x3 inner square is at (6, 4).
• The only spot left for T in the 2nd 3x3 inner square is at (7, 3).

Step 2. There are 4 independent moves.

• The only spot left for C in the 7th column is at (7, 4).
• The only spot left for N in the 4th 3x3 square is at (1, 6).
• The only spot left for N in the 1st 3x3 inner square is at (3, 2).
• The only spot left for O in the 2nd 3x3 inner square is at (6, 3).

Step 3. There are 3 independent moves.

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

Step 4. There is 1 independent move.

• The only spot left for A in the 2nd 3x3 inner square is at (8, 2).

Step 5. There is 1 independent move.

• The only spot left for I in the 2nd 3x3 inner square is at (8, 3).

Step 6. There are 2 independent moves.

• The only spot left for U in the 3rd row is at (1, 3).
• The only spot left for U in the 2nd 3x3 inner square is at (8, 4).

Step 7. There are 3 independent moves.

• The only spot left for D in the 1st 3x3 square is at (3, 3).
• The only spot left for U in the 3rd 3x3 square is at (9, 1).
• The only spot left for U in the 1st 3x3 inner square is at (4, 2).

Step 8. There are 4 independent moves.

• The only spot left for I in the 2nd row is at (1, 2).
• The only spot left for I in the 2nd 3x3 square is at (4, 1).
• The only spot left for D in the 3rd 3x3 square is at (8, 1).
• The only spot left for U in the 5th 3x3 square is at (5, 6).

Step 9. There are 5 independent moves.

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

Step 10. There are 6 independent moves.

• The only spot left for D in the 4th row is at (9, 4).
• The only spot left for E in the 9th row is at (6, 9).
• The only spot left for C in the 2nd 3x3 square is at (5, 1).
• The only spot left for D in the 5th 3x3 square is at (4, 6).
• The only spot left for A in the 6th 3x3 square is at (7, 6).
• The only spot left for T in the 1st 3x3 inner square is at (3, 4).

Step 11. There are 5 independent moves.

• The only spot left for O in the 6th row is at (2, 6).
• The only spot left for U in the 9th row is at (7, 9).
• The only spot left for O in the 5th 3x3 square is at (4, 4).
• The only spot left for I in the 1st 3x3 inner square is at (2, 4).
• The only spot left for T in the 3rd 3x3 inner square is at (4, 7).

Step 12. There are 6 independent moves.

• The only spot left for N in the 7th row is at (8, 7).
• The only spot left for O in the 8th row is at (7, 8).
• The only spot left for O in the 7th 3x3 square is at (3, 9).
• The only spot left for T in the 7th 3x3 square is at (1, 9).
• The only spot left for N in the 3rd 3x3 inner square is at (4, 8).
• The only spot left for I in the 3rd 3x3 inner square is at (3, 7).

Step 13. There are 10 independent moves.

• The only spot left for A in the 7th row is at (9, 7).
• The only spot left for E in the 7th row is at (2, 7).
• The only spot left for D in the 8th row is at (1, 8).
• The only spot left for D in the 9th row is at (5, 9).
• The only spot left for A in the 8th 3x3 square is at (4, 9).
• The only spot left for O in the 8th 3x3 square is at (5, 7).
• The only spot left for I in the 9th 3x3 square is at (9, 9).
• The only spot left for A in the 3rd 3x3 inner square is at (3, 8).
• The only spot left for E in the 4th 3x3 inner square is at (8, 8).
• The only spot left for D in the 4th 3x3 inner square is at (7, 7).

Step 14. There are 4 independent moves.

• The only spot left for U in the 7th row is at (6, 7).
• The only spot left for C in the 8th row is at (6, 8).
• The only spot left for C in the 7th 3x3 square is at (1, 7).
• The only spot left for U in the 3rd 3x3 inner square is at (2, 8).