Diophantine equations over function fields

This paper proves the boundedness of the degrees of at least two components of an arbitrary solution $(x_1,\dots,x_n)$ of the equation
$$ a_1x_1^{s_1}+\dots+a_nx_n^{s_n}=0, $$
where $x_1(t),\dots,x_n(t)$ are pairwise relatively prime polynomials.
Bibliography: 4 titles.