In recent papers the concept of Hartman (measurable) sets was investigated. A subset H of the integers, or more generally, of a topological group G is called Hartman measurable (or simply a Hartman set), if H = ι(M) for some continuous homomorphism ι : G → C, C = ι(G) a compact group, and M ⊆ C a set whose topological boundary ∂M is a null set w.r.t. the Haar measure on C. This concept turned o...