  In a recent paper [El 13], M.E. Kahoui has shown that if $R$ is a polynomial
ring over $\mathbb{C}$, $A$ an $\mathbb{A}^3$-fibration over $R$, and $W$ a
residual variable of $A$ then $A$ is stably polynomial over $R[W]$. In this
article we show that the above result holds over any Noetherian domain $R$
provided the module of differentials $\Omega_R(A)$ of the affine fibration $A$
(which is necessarily a projective $A$-module by a theorem of Asanuma) is a
stably free $A$-module.
