Unique numbers in a row or column of a box
They are a type of “conjugate pair” but that must occur in a row or column, but within a box.
A number that is a candidate in two cells of the same row or column of a box, allowing its exclusion in other cells that can see them. The number “2” is only found in two cells of box 4 in row F. It will necessarily occupy cell F2 or F3 in row F, and therefore the other number “2”s in box 4 can be eliminated.
In the Sudoku below, in box 1, the number “4” is only found in row B, allowing for the exclusions marked in red.
