Unique {0} type 2

The cells {3} form a Unique {0} with the values {1} and {2}. There are exactly two ways of placing the values {1} and {2} in the cells of the Unique {0}, forming two possible configurations.

In both configurations, each row, column or box touched by the Unique {0} contains each of the two values {1} and {2} exactly once. As a result, if one of these two configurations were part of the solution, it could then be replaced by the other one to get a second valid solution.

Because a valid sudoku cannot have more than one solution, none of the two configurations of the Unique {0} can be valid. The only possible way to avoid these two configurations is if one of {4} contains the value {6}.

Other occurrences of the value {6} can therefore be removed from the cells that share a row, column or box with {5}.