“…A thorough treatment is listed in the bibliography, e.g. Sudbery [14], Xu [15], Brackx, Delanghe and Sommen [2], Brackx and Delanghe [3], Avetisyan, Gürlebeck and Sprößig [1], and Morais et al [6,7,9]. The main point in the approach presented in [2,3] as well as Sudbery's formula [14] is the construction of harmonic conjugates in R 4 "function by function".…”