For $K\subset \mathbb C$ a compact subset and $\mu$ a positive finite Bore1
measure supported on $K,$ let $R^\infty (K,\mu)$ be the weak-star closure in
$L^\infty (\mu)$ of rational functions with poles off $K.$ We show that if
$R^\infty (K,\mu)$ has no non-trivial $L^\infty$ summands and $f\in R^\infty
(K,\mu),$ then $f$ is invertible in $R^\infty (K,\mu)$ if and only if Chaumat's
map for $K$ and $\mu$ applied to $f$ is bounded away from zero on the envelope
with respect to $K$ and $\mu.$ The result proves the conjecture $\diamond$
posed by J. Dudziak in 1984.Comment: arXiv admin note: text overlap with arXiv:2212.1081