  We study the structure of length four polynomial automorphisms of $R[X,Y]$
when $R$ is a UFD. The results from this study are used to prove that if
$\text{SL}_m(R[X_1,X_2,..., X_n]) = \text{E}_m(R[X_1,X_2,..., X_n])$ for all
$n, m \ge 0$ then all length four polynomial automorphisms of $R[X,Y]$ that are
conjugates are stably tame.
