gsf wrote:Lummox JR wrote:No indeed. Trial and error has a specific placement to prove true or false; this does not. This method compares possible sets to determine which interfere with each other, and which can never be chosen. Based on that it can look for 1) digits which never appear in a certain position, or even better 2) digits which always appear in a certain position.

are you saying trial and error is limited to "does this move solve the puzzle"?

Absolutely not. I'm saying trial-and-error is limited to:

1) Does this move cause a contradiction?

2) Does this set of moves, one of which must be true, prove another move false?

3) Does this set of moves, one of which must be true, prove another move true?

Clearly Brendan's technique is not T&E, although it may be making deductions with similar results, because it has a pattern. It's analyzing a convergence of two columns or rows, and finding cases that can never work. If you consider that T&E, you could say the same of coloring, X-wing, or any other technique. (Indeed all logical techniques have an if-then factor, but the easier ones are all refined in some way. If the term trial and error is to have meaning at all, you need to draw the line somwhere.)

Another major reason this could not be considered true T&E is that it does not rely on having a specific placement to prove or disprove. It merely applies a pattern and looks for eliminations based on that, as all easier techniques do.