“…Let d(G) denote the maximal length of a zero-sum free sequence over G. Then d(G) + 1 is the Davenport constant of G, a classical constant from Combinatorial Number Theory (for surveys and historical comments, the reader is referred to [3], [8,Chapter 5], [7]). In general, the precise value of d(G) (in terms of the group invariants of G) and the structure of the extremal sequences is unknown, see [12,1,13,10,11,4,14,15,9] for recent progress.…”