In this paper we introduce a set, denoted by Dn(A), for every commutative ringAand every positive integern. It is shown that the elements of this set can be used to give an explicit description of the class Hn(A) introduced in6. We deduce that each polynomial map of the formF=X+HwithH∈Hn(A) can be written as a finite product of automorphisms of the form exp(D), where eachDis a locally nilpotent derivation satisfyingD2(Xi)=0 for alli. Furthermore we deduce that all suchFs are stably tame.