Medium Puzzle #42 - 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	5			8	6					Medium Puzzle #42 - November 11, 2005
2		1	6			7	4				Original puzzle as published © joe-ks.com
3			8	9			1	7
4	8			3	1			4	9
5	1	2			6	8			7
6		6	4			9	2
7			3	6			8	1
8				8	9			6	3
9					5				4
	A	B	C	D	E	F	G	H	I
1	4	5		1	8	6					Step 1: #1 is in Rows 2 & 3: #1 MUST go in Cell D1...
2		1	6			7	4
3			8	9			1	7			Step 2: #2 is in Rows 5 & 6: #2 MUST go in Cell F4...
4	8			3	1	2		4	9
5	1	2			6	8			7		Step 3: #3 is in Rows 7 & 8: #3 MUST go in Cell F9
6		6	4			9	2				(cf #3 in Column D @ D4 excludes use of Cell D9)
7			3	6			8	1
8				8	9			6	3
9					5	3			4
	A	B	C	D	E	F	G	H	I
1	4	5		1	8	6					Step 4: #6 is in Columns B & C: #6 MUST go in Cell A9
2		1	6			7	4				(#6 in Row 7 @ D7 excludes use of Cell A7, &
3			8	9			1	7			#6 in Row 8 @ H8 excludes use of Cell A8)
4	8			3	1	2		4	9
5	1	2			6	8			7
6		6	4			9	2
7			3	6			8	1
8				8	9			6	3
9	6				5	3			4
	A	B	C	D	E	F	G	H	I
1	4	5	7	1	8	6					Step 5: Block EE needs #4: #4 MUST go in Cell D5
2	9	1	6			7	4				(#4 in Row 6 @ C6 excludes use of Cells D6 & E6)
3			8	9			1	7
4	8			3	1	2		4	9		Step 6: #7 is in Rows 2 & 3: #7 MUST go in Cell C1...
5	1	2		4	6	8			7
6		6	4			9	2				Step 7: Block AA needs #9: #9 MUST go in Cell A2
7			3	6			8	1			(#9 in Row 3 @ D3 excludes use of Cells A3 & B3)
8				8	9			6	3		Step 8: #8 is in Rows 7 & 8: #8 MUST go in Cell B9
9	6	8			5	3			4		(#8 in Column C @ C3 excludes use of Cell C9)
	A	B	C	D	E	F	G	H	I
1	4	5	7	1	8	6					Step 8: Complete Block AA: need #s 2 & 3…
2	9	1	6			7	4				#2 can't go in Cell B3 (cf #2 in Column B @ B5), so
3	2	3	8	9			1	7			#2 MUST go in Cell A3, & therefore #3 MUST go in Cell B3
4	8	7		3	1	2		4	9
5	1	2		4	6	8			7		Step 9: Complete  Block EE: need #s 5 & 7…
6		6	4	5	7	9	2				#5 can't go in Cell E6 (cf #5 in Column E @ E9), so
7			3	6			8	1			#5 MUST go in Cell D6, & therefore #7 MUST go in Cell E6
8				8	9			6	3		Step 10: #7 is now in Rows 5 & 6: #7 MUST go in Cell B4
9	6	8			5	3			4		(#7 in Column C @ C1 excludes use of Cell C4)
	A	B	C	D	E	F	G	H	I
1	4	5	7	1	8	6					Step 10: Block DD needs #3: #3 MUST go in Cell A6
2	9	1	6			7	4				(#3 in Column C @ C7 excludes use of Cell C4 & C5)
3	2	3	8	9			1	7
4	8	7	5	3	1	2		4	9		Step 11: Complete Block DD: need #s 5 & 9…
5	1	2	9	4	6	8			7		#9 can't go in Cell C4 (cf #9 in Row 4 @ I4), so
6	3	6	4	5	7	9	2				#9 MUST go in Cell C5, & therefore #5 MUST go in Cell C4
7			3	6			8	1
8				8	9			6	3
9	6	8			5	3			4
	A	B	C	D	E	F	G	H	I
1	4	5	7	1	8	6					Step 12: Complete Column D: need #s 2 & 7…
2	9	1	6	2		7	4				#7 can't go in Cell D2 (cf #7 in Row 2 @ F2), so
3	2	3	8	9			1	7	6		#7 MUST go in Cell D9, & therefore #2 MUST go in Cell D2
4	8	7	5	3	1	2	6	4	9
5	1	2	9	4	6	8			7		Step 13: Complete Row 4: #6 MUST go in Cell G4...
6	3	6	4	5	7	9	2
7			3	6			8	1			Step 14: #6 is now in Columns G & H: #6 MUST go in Cell I3
8				8	9			6	3		(#6 in Row 1 @ F1 excludes use of Cell I1, &
9	6	8		7	5	3			4		#6 in Row 2 @ C2 excludes use of Cell I2)
	A	B	C	D	E	F	G	H	I
1	4	5	7	1	8	6					Step 15: Complete Row 6: need #s 1 & 8…
2	9	1	6	2		7	4				#1 can't go in Cell H6 (cf #1 in Column H @ H7), so
3	2	3	8	9	4	5	1	7	6		#1 MUST go in Cell I6, & therefore #8 MUST go in Cell H6
4	8	7	5	3	1	2	6	4	9
5	1	2	9	4	6	8			7		Step 16: Complete Row 3: need #s 4 & 5…
6	3	6	4	5	7	9	2	8	1		#5 can't go in Cell E3 (cf #5 in Column # @ E9), so
7			3	6			8	1			#5 MUST go in Cell F3, & therefore #4 MUST go in Cell E3
8				8	9			6	3
9	6	8		7	5	3			4
	A	B	C	D	E	F	G	H	I
1	4	5	7	1	8	6					Step 17: Complete Block BB: #3 MUST go in Cell E2...
2	9	1	6	2	3	7	4
3	2	3	8	9	4	5	1	7	6		Step 18: Complete Column E: #2 MUST go in Cell E7…
4	8	7	5	3	1	2	6	4	9
5	1	2	9	4	6	8			7
6	3	6	4	5	7	9	2	8	1
7			3	6	2		8	1
8				8	9			6	3
9	6	8		7	5	3			4
	A	B	C	D	E	F	G	H	I
1	4	5	7	1	8	6					Step 19: Complete Block HH: need #s 1 & 4…
2	9	1	6	2	3	7	4	5	8		#1 can't go in Cell F7 (cf #1 in Row 7 @ H7), so
3	2	3	8	9	4	5	1	7	6		#1 MUST go in Cell F8, & therefore #4 MUST go in Cell F7
4	8	7	5	3	1	2	6	4	9
5	1	2	9	4	6	8			7		Step 20: Complete Row 2: need #s 5 & 8…
6	3	6	4	5	7	9	2	8	1		#8 can't go in Cell H2 (cf #8 in Column H @ H6), so
7			3	6	2	4	8	1			#8 MUST go in Cell I2, & therefore #5 MUST go in Cell H2
8				8	9	1		6	3
9	6	8		7	5	3			4
	A	B	C	D	E	F	G	H	I
1	4	5	7	1	8	6					Step 21: Complete Block FF: need #s 3 & 5…
2	9	1	6	2	3	7	4	5	8		#5 can't go in Cell H5 (cf #5 in Column H @ H2), so
3	2	3	8	9	4	5	1	7	6