Dan Rice's Weblog

Two and Three in a Bed
So far, I‘ve discussed rules that take place within a single group — a row, column, or box. All of these rules can be summarized as follows: * If N cells together contain exactly N values, remove those values from the other cells of the group * If N values can only appear in exactly N calls, remove the other values from those cells When N is 1, the first rule is the rule of elimination; when N is 2, it‘s the rule of pairs, when N is three it‘s the rule of (interlocking) triples, etc. When N is 1, the second rule is the rule of uniqueness. I don‘t have a good name for the second rule when N is larger than 1. Any suggestions? Now we are ready to look at rules that look outside a single group, and deal with the interactions between groups. In particular, today‘s rule deals with the interaction between a box and the rows and columns that intersect it... The rest of this entry has been moved here.