In three phases of a helpmate twomover the roles of three thematic white pieces are cyclically changed: each one mates once and is captured twice. A true cycle occurs when each piece is once captured on the first, once on the second black move, and once survives and eventually mates. Further, for a pure cycle the first white move must be an active sacrifice of a thematic piece.
See also: Cyclic Zilahi.
Feather, Christopher John