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.