Lačny theme

The Lačny theme compares phases of a composition. A phase is a distinct part of the play, such as replies prepared in the diagram before White's correct first move, a try that nearly solves, or the actual solution. The same Black defenses occur in each phase, but White's mating replies change in a cycle.

Basic scheme

Lowercase letters a, b, and c label three Black defenses, while A, B, and C label three White mates. They are not chess notation or actual moves; they simply display the relationships.

1. First phase: a permits A, b permits B, and c permits C.
2. Second phase: a permits B, b permits C, and c permits A.

Each mate shifts to the next defense and, after the third, returns to the first. A complete three-phase Lačny adds another rotation: a permits C, b permits A, and c permits B.

It is not enough for the mating moves merely to differ between phases. The defenses must remain the same and the cyclic reassignment must be recognizable. Each branch also needs one effective reply; if two mates work against the same defense, a dual may spoil the scheme's precision.