  Let Y be a surface with only finitely many singularities all of which are
cusps. A set of cusps on Y is called three-divisible, if there is a cyclic
global triple cover of Y branched precisely over these cusps. The aim of this
note is to determine the equations of surfaces $Y \subset P_3$ of degrees $\leq
6$ carrying a minimal, non-empty, three-divisible set.
