The purple highlighted square is missing the number 7. the red highlighted 7 eliminates
two of the empty tiles. One of the remaining two empty tiles must be the 7. Since they are both on the
same row, no matter which one it is, nothing else on this row can be a 7.
The gray highlighted column below is missing the number 7. The pink highlighted 7's eliminate
all but one of the empty tiles. The remaining empty tile must be a 7. |