Blog about chess problems
After black defense, White seems to have several mates or possibilities. However, for various reasons, only one possibility passes.
Generally speaking, a partial dual avoidance happens when the mate which is prevented in one scenario and passed in the other.
Three or more mates appearing in cyclic pairs (one real and one apparent) in such a way that the apparent mate appears as real in the next variation, and the apparent mate in the last variation closes the cycle becoming real in the first variation. It is also possible to cyclically avoid the dual in triplets (one real and two apparent).
The mate that is prevented in one variation does not appear in the other variation.
Adabashev, Mark
Shakhmaty v SSSR, 1938
1st Prize
mate in 2 moves
An interference between line-pieces of unlike-motion and of the same color, forced by a sacrifice on the critical (interference) square.