  We provide a proof of a formula conjectured in \cite{OU93} for some
coefficients relevant in the principal vertex operator construction of a
simply-laced affine algebra $\gh$. These coefficients are important for the
study of the topological charges of the solitons of affine Toda theories, and
the construction of representations of non-simply-laced $\gh$ and their
associated Toda solitons.
