we shall continue to use mutipli cative notation for our general work on cyclic groups, even though they are abelian.
there is a weak but very important converse of Theorem 6.1 which will be discussed in greater detail later. Namely, it can be shown that every "sufficiently small" abelian group can be built up from cyclic groups in a certain fashion. Thus cyclic groups are very fundamental in the study of abelian groups. Cyclic groups are sort of elementary types of abelian groups. One would hope that a portion of an elementary type is again an elementary type. The next theorem shows that this is indeed so. We first give a seemingly trivial but very fundamental number-theoretic lemma.