Duncan's SuDoku Solver
This is a screenshot
Rows and Columns (Triple):
Occurances of a particular Possible
occur three times or less in their Rows
and are also aligned in Columns
(or appear three times or less in their Columns and are also aligned in Rows).
In this example, the 9's (coloured grey) occur three times or less in their Rows and are also aligned in Columns.
Because of this, for each of the Rows A, C, and J, there are only three Squares where a 9 can be a Solution - namely those in Columns 3, 4, and 8.
If the 9 for Row A is in Column 3, then there are only two Squares left for each of the remaining Rows - those for Columns 4, and 8.
If the 9 for Row C is in Column 8, then there is only one Square left for the remaining Row - that for Column 4.
Because there is now a 9 in place for Columns 3, 4, and 8, there cannot be any other 9's in those Columns.
This logic works whatever order you choose the Rows and Columns.