When there are multiple cells in a unit
that have to contain just one of a group of candidates
these multiple cells are considered a Pseudo Cell
A Pseudo Cell can be considered like an ordinary cell when searching for a locked set
, strong links
or weak links
The blue cells in Figure 1 are an example of a Pseudo Cell
containing candidates 2 and 9 in row 4.
The Unique Rectangle
in this example, made up of the blue and green cells, mandates that not both the 5 and the 7 can be used in the blue cells in row four.
The two blue cells in row four will need to be filled with a 5 or a 7 and one other value. The other value will have to come from the candidates 2 and 9 which are the only other candidates in the blue cells.
This creates a pseudo cell in row 4 that contains the candidates 2 and 9.
In this example the pseudo cell (the two blue cells) has been used with the red cell to create a naked set