“…In [10], W. Gao, A. Geroldinger and D. J. Grynkiewicz showed that this result is multiplicative, extending our conclusion to the groups C 2 n for a composite number n. In [17], W. A. Schmid discusses the case C n × C m , where n|m. Not much is known about groups of rank exceeding 2, only few specific cases (see, for example, [17]).…”