Dual

Dual (from lat. Dualis - double; double blow)

In the chess problem - a partial side solution , that is, the presence of duality in the white moves, starting from the 2nd or subsequent moves. Distinguish between strong and weak duals:

• Strong dual - performing tasks in thematic versions in a way different from the author's. As a rule, the task at the same time loses its right to exist before the publication in the corrected form.
• Weak dual - the presence of duality in White's moves in secondary nematic variants, as well as two or more refutations of thematic false traces . It usually turns out negatively on the assessment of the problem. In the English school, compositions were considered unacceptable even duals in secondary versions.

In a chess sketch, a dual means that a piece reaches a certain field in almost the same way (for example, Kre4 - Kre5 - Kd6 or Kre4 - Kd5 - Kd6) or the rearrangement of moves without violating the design of the sketch. Such a dual can also negatively affect the assessment of the sketch.