Virtual play

Virtual play consists of variations that a composition contains and invites the solver to examine, but that do not belong to the actual play begun by the correct key, the first move that starts the solution. A phase is a distinct section of content made up of a coherent group of variations. Comparing phases reveals changes in replies, mating moves, meaning moves that leave the king attacked with no legal reply, or piece functions.

Common forms

• Set play shows what would happen if the side due to move could pass. The replies are already prepared in the diagram before the real first move.
• Try play begins with a move that almost solves the problem but fails to one defense, called the refutation. The variations following that try still contribute to the thematic content.

The term is not equally broad in every tradition. The composition Codex includes set play, try play, and similar material under virtual play, while some glossaries use it more narrowly as another name for try play. The source or composer's usage therefore matters.

Virtual play becomes most meaningful when compared with the actual play required by the stipulation, the task written beside the position. The same defenses may receive different answers in several phases. That comparison underlies changed-play themes such as the Zagoruiko theme.