Primary decompositions in varieties of commutative diassociative loops

Abstract

The decomposition theorem for torsion abelian groups holds analogously for torsion commutative diassociative loops. With this theorem in mind, we investigate commutative diassociative loops satisfying the additional condition (trivially satisfied in the abelian group case) that all $n$th powers are central, for a fixed $n$. For $n=2$, we get precisely commutative $C$ loops. For $n=3$, a prominent variety is that of commutative Moufang loops. Many analogies between commutative C and Moufang loops have been noted in the literature, often obtained by interchanging the role of the primes 2 and 3. We show that the correct encompassing variety for these two classes of loops is the variety of commutative RIF loops. In particular, when $Q$ is a commutative RIF loop: all squares in $Q$ are Moufang elements, all cubes are $C$ elements, Moufang elements of $Q$ form a normal subloop $M_0(Q)$ such that $Q/M_0(Q)$ is a C loop of exponent 2 (a Steiner loop), C elements of $L$ form a normal subloop $C_0(Q)$ such that $Q/C_0(Q)$ is a Moufang loop of exponent 3. Since squares (resp. cubes) are central in commutative C (resp. Moufang) loops, it follows that $Q$ modulo its center is of exponent 6. Returning to the decomposition theorem, we find that every torsion, commutative RIF loop is a direct product of a C 2-loop, a Moufang 3-loop, and an abelian group with each element of order prime to 6. We also discuss Moufang elements, and a class of quasigroups associated with commutative RIF loops.