## Locked Candidates (type 2) question

Gilbert
New kid on the Grid
Posts: 2
Joined: Thu Jul 13, 2006 12:32 pm
Location: NYC

### Locked Candidates (type 2) question

Dear Sudocue fans,

Under "Sudoku Solving Guide", there is an example for "Locked Candidates (type 2)". Could someone please explain why box 5 can't have 7 in Column 4 or Column 6 (highlighted in red). With all the given digits shown, I somehow failed to understand this topic.

Gilbert
Gilbert
David Bryant
Gold Member
Posts: 86
Joined: Fri Jan 20, 2006 6:21 pm
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### "Locked candidates (type 2)"

Hi, Gilbert! I'll try to explain it for you.

In the example column 5 has four cells filled in, and five empty cells (r2c5, r4c5, r5c5, r6c5, and r8c5). There's a "7" at r2c3, and another "7" at r8c9.

-- Clearly the "7" in column 5 cannot appear at r2c5, because of the "7" at r2c3.

-- Similarly, the "7" in column 5 cannot appear at r8c5, because of the "7" at r8c9.

-- Therefore the "7" in column 5 must appear at r4c5, r5c5, or r6c5. In other words, the "7" in column 5 has to lie in box 5.

-- But saying that the "7" in column 5 lies in box 5 means the same thing as saying that the "7" in box 5 lies in column 5. And since the "7" in box 5 has to be in column 5, it can't possibly be in column 4 or in column 6.

I hope that clears it up for you. dcb
Gilbert
New kid on the Grid
Posts: 2
Joined: Thu Jul 13, 2006 12:32 pm
Location: NYC
Hey David, I finally got it, many thanks! I think I am getting hooked with Soducue now.
Gilbert