Unavoidable Set

An unavoidable set is a Deadly Pattern from the point of view of a puzzle maker, or somebody who likes to investigate solution grids.

Take the following example:

. 1 . . . 2 . . .	. 2 . . 1 . . . .	. . . . . . . . .
. 2 1 . . . . . .	. . . . . . . . .	. . . . . . . . .
. . . . . . . . .	. . . . . . . . .	. . . . . . . . .

If there were no givens in any of these 6 cells, the solver would eventually reach a point were a choice must be made how to place digits 1 and 2 in them. The conclusion would be that the puzzle has 2 possible solutions. It is unavoidable for the puzzle maker to place at least one given in one of these cells.