  It has been proved several times in the literature that a polynomial map from
$C^2$ to $C$ with irreducible rational fibers cannot be a component of a
counterexample to the Jacobian Conjecture. This note points out that this
result is empty: it is implicit in 1980 work of Miyanish and Sugie that such a
polynomial is equivalent to $f(x,y)=x$ by a polynomial automorphism of $C^2$.
