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Medium Sudoku-15up Group Puzzle
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The small superscript in each undetermined location is the step number at which the location must be fill before all of the locations with subsequent step numbers can be determined. A detailed description of the moves in each step is given below.

Display the puzzle with superscripts showing just the step number for the first few steps in their empty grid locations.

See the puzzle answer grid.

Deductive steps to solve the puzzle

The moves within each step may be done in any order.

All of the moves within a particular step must be done before all of the moves in the subsequent step can be guaranteed to be completed.

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 .

Step 1. There are 40 independent moves.

• The only spot left for 2 in the 1st row is at (10, 1).
• The only spot left for A in the 4th row is at (4, 4).
• The only spot left for 9 in the 5th row is at (3, 5).
• The only spot left for 9 in the 7th row is at (11, 7).
• The only spot left for 6 in the 7th row is at (6, 7).
• The only spot left for 8 in the 8th row is at (12, 8).
• The only spot left for 2 in the 9th row is at (1, 9).
• The only spot left for 7 in the 11th row is at (1, 11).
• The only spot left for 1 in the 12th row is at (13, 12).
• The only spot left for 2 in the 12th row is at (12, 12).
• The only spot left for A in the 13th row is at (6, 13).
• The only spot left for 8 in the 2nd column is at (2, 13).
• The only spot left for E in the 9th column is at (9, 1).
• The only spot left for 8 in the 1st 3x5 rectangle is at (1, 4).
• The only spot left for 6 in the 1st 3x5 rectangle is at (3, 2).
• The only spot left for C in the 2nd 3x5 rectangle is at (4, 5).
• The only spot left for 2 in the 2nd 3x5 rectangle is at (6, 2).
• The only spot left for 0 in the 3rd 3x5 rectangle is at (7, 4).
• The only spot left for 5 in the 3rd 3x5 rectangle is at (9, 3).
• The only spot left for 9 in the 3rd 3x5 rectangle is at (8, 2).
• The only spot left for 0 in the 4th 3x5 rectangle is at (11, 3).
• The only spot left for 9 in the 5th 3x5 rectangle is at (14, 3).
• The only spot left for 3 in the 5th 3x5 rectangle is at (15, 2).
• The only spot left for 4 in the 6th 3x5 rectangle is at (1, 6).
• The only spot left for 9 in the 7th 3x5 rectangle is at (5, 10).
• The only spot left for 2 in the 7th 3x5 rectangle is at (4, 10).
• The only spot left for 1 in the 8th 3x5 rectangle is at (7, 9).
• The only spot left for C in the 8th 3x5 rectangle is at (8, 7).
• The only spot left for A in the 9th 3x5 rectangle is at (12, 9).
• The only spot left for 6 in the 10th 3x5 rectangle is at (14, 8).
• The only spot left for 0 in the 10th 3x5 rectangle is at (15, 6).
• The only spot left for A in the 11th 3x5 rectangle is at (3, 11).
• The only spot left for 4 in the 12th 3x5 rectangle is at (4, 14).
• The only spot left for 1 in the 12th 3x5 rectangle is at (4, 11).
• The only spot left for 7 in the 13th 3x5 rectangle is at (7, 15).
• The only spot left for 4 in the 13th 3x5 rectangle is at (8, 12).
• The only spot left for 5 in the 13th 3x5 rectangle is at (8, 11).
• The only spot left for D in the 14th 3x5 rectangle is at (12, 15).
• The only spot left for 6 in the 14th 3x5 rectangle is at (10, 14).
• The only spot left for 9 in the 15th 3x5 rectangle is at (13, 15).

Step 2. There are 24 independent moves.

• The only spot left for A in the 1st row is at (15, 1).
• The only spot left for B in the 1st row is at (1, 1).
• The only spot left for 0 in the 5th row is at (2, 5).
• The only spot left for 6 in the 13th row is at (5, 13).
• The only spot left for 3 in the 14th row is at (7, 14).
• The only spot left for 7 in the 5th column is at (5, 3).
• The only spot left for B in the 10th column is at (10, 11).
• The only spot left for C in the 14th column is at (14, 11).
• The only spot left for 1 in the 1st 3x5 rectangle is at (2, 2).
• The only spot left for 3 in the 2nd 3x5 rectangle is at (5, 4).
• The only spot left for A in the 3rd 3x5 rectangle is at (9, 5).
• The only spot left for B in the 4th 3x5 rectangle is at (12, 4).
• The only spot left for 7 in the 4th 3x5 rectangle is at (12, 2).
• The only spot left for C in the 5th 3x5 rectangle is at (15, 3).
• The only spot left for 0 in the 5th 3x5 rectangle is at (14, 1).
• The only spot left for 3 in the 7th 3x5 rectangle is at (4, 6).
• The only spot left for B in the 9th 3x5 rectangle is at (11, 10).
• The only spot left for 1 in the 9th 3x5 rectangle is at (10, 8).
• The only spot left for E in the 10th 3x5 rectangle is at (14, 10).
• The only spot left for 2 in the 11th 3x5 rectangle is at (2, 15).
• The only spot left for 6 in the 11th 3x5 rectangle is at (1, 15).
• The only spot left for 8 in the 12th 3x5 rectangle is at (6, 12).
• The only spot left for E in the 13th 3x5 rectangle is at (8, 13).
• The only spot left for 3 in the 15th 3x5 rectangle is at (14, 12).

Step 3. There are 20 independent moves.

• The only spot left for 7 in the 6th row is at (6, 6).
• The only spot left for 5 in the 8th row is at (6, 8).
• The only spot left for E in the 11th row is at (15, 11).
• The only spot left for B in the 12th row is at (5, 12).
• The only spot left for 0 in the 1st column is at (1, 14).
• The only spot left for B in the 2nd column is at (2, 7).
• The only spot left for 3 in the 10th column is at (10, 9).
• The only spot left for E in the 12th column is at (12, 6).
• The only spot left for B in the 2nd 3x5 rectangle is at (6, 5).
• The only spot left for E in the 4th 3x5 rectangle is at (10, 2).
• The only spot left for 7 in the 5th 3x5 rectangle is at (15, 5).
• The only spot left for 1 in the 6th 3x5 rectangle is at (3, 10).
• The only spot left for 0 in the 6th 3x5 rectangle is at (3, 7).
• The only spot left for 7 in the 9th 3x5 rectangle is at (11, 8).
• The only spot left for 5 in the 9th 3x5 rectangle is at (10, 6).
• The only spot left for B in the 11th 3x5 rectangle is at (3, 14).
• The only spot left for B in the 13th 3x5 rectangle is at (7, 13).
• The only spot left for 3 in the 14th 3x5 rectangle is at (11, 13).
• The only spot left for E in the 14th 3x5 rectangle is at (11, 12).
• The only spot left for B in the 15th 3x5 rectangle is at (15, 15).

Step 4. There are 6 independent moves.

• The only spot left for 7 in the 9th row is at (9, 9).
• The only spot left for 8 in the 15th column is at (15, 9).
• The only spot left for 7 in the 6th 3x5 rectangle is at (2, 10).
• The only spot left for 3 in the 6th 3x5 rectangle is at (3, 8).
• The only spot left for E in the 12th 3x5 rectangle is at (5, 15).
• The only spot left for 8 in the 15th 3x5 rectangle is at (13, 11).

Step 5. There are 2 independent moves.

• The only spot left for 8 in the 8th 3x5 rectangle is at (9, 10).
• The only spot left for 7 in the 10th 3x5 rectangle is at (13, 7).

Step 6. There are 2 independent moves.

• The only spot left for 3 in the 8th 3x5 rectangle is at (9, 7).
• The only spot left for 3 in the 10th 3x5 rectangle is at (13, 10).

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