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Medium Puzzle #37 - One Possible Solution Approach…
NB:  There is only one final solution to this Sudoku puzzle…
A B C D E F G H I
1                  
2 AA BB CC Reference to 3x3 Blocks AA, BB & CC
3                  
4                  
5 DD EE FF Reference to 3x3 Blocks DD, EE & FF
6                  
7                  
8 GG HH II Reference to 3x3 Blocks GG, HH & II
9                  
A B C D E F G H I
1       4       6   Medium Puzzle #37 - November 6, 2005
2 6   4   3   2   8 Original puzzle as published © joe-ks.com
3 2 3       6     7
4 8   7       4    
5 4 9 3 6 5 7 8 1 2
6 5   2       3    
7 3 8       4     9
8 9   6   1   7   4
9       2       3  
A B C D E F G H I
1       4       6 3 Step 1: #4 is in Columns A & C: #4 MUST go in Cell B9
2 6   4   3   2   8      (#4 in Row 8 @ I9 excludes use of Cell B8)
3 2 3       6     7
4 8   7       4    
5 4 9 3 6 5 7 8 1 2 Step 2: #3 is in Columns G & H: #3 MUST go in Cell I1...
6 5   2       3    
7 3 8       4     9
8 9   6   1   7   4
9   4   2       3  
A B C D E F G H I
1       4       6 3 Step 3: #4 is in Rows 1 & 2: #4 MUST go in Cell H3
2 6   4   3   2   8      (#4 in Column G @ G4 excludes use of Cell G3)
3 2 3       6   4 7
4 8   7       4    
5 4 9 3 6 5 7 8 1 2
6 5   2       3    
7 3 8       4     9
8 9   6   1   7   4
9   4   2       3  
A B C D E F G H I
1       4       6 3 Step 4: #7 is in Column G & I: #7 MUST go in Cell H6
2 6   4   3   2   8      (#7 in Row 4 @ C4 exlcudes use of Cell H4)
3 2 3       6   4 7
4 8   7       4     Step 5: Block GG needs #2: #2 MUST go in Cell B8
5 4 9 3 6 5 7 8 1 2      (#2 in Column C @ C6 excludes use of Cells C7 & C9, &
6 5   2       3 7          #2 in Row 9 @ D9 further exludes use of Cell A9)
7 3 8       4   2 9
8 9 2 6   1   7   4 Step 6: #2 is now in Rows 8 & 9: #2 MUST go in Cell H7
9   4   2       3        (#2 in Column G @ G2 excludes use of Cell G7)
A B C D E F G H I
1       4       6 3 Step 7: #4 is in Columns D & F: #4 MUST go in Cell E6
2 6   4   3   2   8
3 2 3       6   4 7
4 8   7       4     Step 8: #8 is in Columns G & I: #8 MUST go in Cell H8...
5 4 9 3 6 5 7 8 1 2     (#4 in Row 4 @ G4 excludes use of Cell E4)
6 5   2   4   3 7  
7 3 8       4   2 9
8 9 2 6   1   7 8 4
9   4   2       3  
A B C D E F G H I
1 1     4       6 3 Step 9: Block GG needs #7: #8 MUST go in Cell A9
2 6   4   3   2   8      (#7 in Column C @ C4 excludes use of Cells C7 & C9)
3 2 3       6 1 4 7
4 8   7       4     Step 10: Complete Column A: #1 MUST go in Cell A1...
5 4 9 3 6 5 7 8 1 2
6 5   2   4   3 7   Step 11: Block CC needs #1: #1 MUST go in Cell G3
7 3 8       4   2 9      (#1 from Step 10 @ A1 excludes use of Cell G1, &
8 9 2 6   1   7 8 4      (#1 in Column H @ H5 excludes use of Cell H2)
9 7 4   2       3  
A B C D E F G H I
1 1     4     9 6 3 Step 12: Clock FF needs #9: #9 MUST go in Cell H4
2 6   4   3   2   8      (#9 in Column I @ I7 excludes use of Cells I4 & I6)
3 2 3       6 1 4 7
4 8   7       4 9   Step 13: #9 is now in Columns H & I: #9 MUST go in Cell G1
5 4 9 3 6 5 7 8 1 2
6 5   2   4   3 7  
7 3 8       4   2 9
8 9 2 6   1   7 8 4
9 7 4   2       3  
A B C D E F G H I
1 1     4     9 6 3 Step 14: Complete Block CC: #5 MUST go in Cell H2...
2 6   4   3   2 5 8
3 2 3       6 1 4 7 Step 15: Complete Block FF: need #s 5 & 6…
4 8 6 7       4 9 5      #5 can't go in Cell I6 (cf #5 in Row 6 @ A6), so
5 4 9 3 6 5 7 8 1 2      #5 MUST go in Cell I4, & therefore #6 MUST go in Cell I6
6 5   2   4   3 7 6
7 3 8       4   2 9 Step 16: #6 is now in Rows 5 & 6: #6 MUST go in Cell B4...
8 9 2 6   1   7 8 4
9 7 4   2       3  
A B C D E F G H I
1 1     4     9 6 3 Step 17: Complete Block DD: #1 MUST go in Cell B6...
2 6   4   3   2 5 8
3 2 3       6 1 4 7 Step 18: #1 is in Columns G & H: #1 MUST go in Cell I9...
4 8 6 7       4 9 5
5 4 9 3 6 5 7 8 1 2 Step 19: #1 is now in Rows 8 & 9: #1 MUST go in Cell C7...
6 5 1 2   4   3 7 6
7 3 8 1     4   2 9 Step 20: Complete Block GG; #5 MUST go in Cell C9...
8 9 2 6   1   7 8 4
9 7 4 5 2       3 1
A B C D E F G H I
1 1     4     9 6 3 Step 21: Complete Block II: Need #s 5 & 6…
2 6   4   3   2 5 8      #5 can't go in Cell G9 (cf #5 from Step 20 in Row 9 @ C9)
3 2 3       6 1 4 7      so #5 MUST go in Cell G7, & therefore #6 MUST go in G9
4 8 6 7       4 9 5
5 4 9 3 6 5 7 8 1 2 Step 22: #6 is now in Rows 8 & 9: #6 MUST go in Cell E7
6 5 1 2   4   3 7 6      (#6 in Column D @ D5 excludes use of Cell D7)
7 3 8 1 7 6 4 5 2 9
8 9 2 6   1   7 8 4 Step 23: #7 is in Rows 8 & 9: #7 MUST go in Cell D7...
9 7 4 5 2     6 3 1
A B C D E F G H I
1 1 5</