by Ruud » Wed Apr 12, 2006 11:10 pm
Hi Keith,
The block-block technique is usually combined with the rowcol-block technique. (block = box)
Other terms used are locked candidates, pointing pairs, line-box interactions (my favorite)
With line-box interactions, you look for a row or column with all candidates in a single box. You can then remove the remaining candidates in that box. You can also look for a box with all candidates in a single row or column (a pointing pair). Then you can eliminate the remaining candidates on that row or column.
block-block is basically the same technique, but it looks at 2 boxes in a chute (3x9 region) with candidates for only 2 rows or columns in that chute. When you find it, eliminate the remaining candidates in those 2 rows/columns (in the 3rd box)
Now think of this: When you find 2 boxes with candidates in only 2 rows/columns, the 3rd row/column must have all candidates in the 3rd box: a line-box interaction. These techniques, like many other patterns, are complementary.
I hope this explanation did help.
Ruud.
