Sudoku Discussions: A little tip to help solve the puzzles

Sudoku Discussions: A little tip to help solve the puzzles: "Now, at the more tactical level:

1 - if, let's say 3-9, 3-9 appear in the same row (or column), then neither 3 or 9 can occur anywhere else in that row (column). If a pair like that occurs in a 3x3 box, then those values cannot appear anywhere else in that 3x3 box.

If a triple occurs (say 3-6-9) three times in the same column (row, 3x3 box), then those three values cannot occur anywhere else in that column (row, 3x3 box).

NOTE that these numbers must occur without any additional values (e.g, 2-4, and 2-4-7 does not tell you anything - you can't assume anything special about 2 and 4).

I usually mark the values that _can_ occur in an empty entry. Then I look at a row (column, 3x3 box) and see if a value occurs in only one entry (then it has to go there), or if I'm looking at a row or column, if it occurs more than once, but only in a single 3x3 box.

As noted by john mcintosh, three entries that involve three possible numbers (e.g., 1-2, 1-3, 2-3) occurring in a row, column or 3x3 box, also allow you to eliminate those values from occurring anywhere else in that row, column, or 3x3 box.

I hope this hasn't been too confusing. It would be nice if we had a standard notation and terminology as does chess.

I have found that using the techniques above, it has never been necessary to resort to bifurcation. In fact, I've not found a case where bifurcation was helpful (the chain of logic was too long and turned the approach into a form of restricted guessing). It could be that I've just done the wrong puzzles and that eventually I'll hit one where bifurcation is necessary and works, however, I think that would indicate an ill-composed puzzle. "

Sudoku is addictive and helps take your mind off the day