Local ABC theorems for analytic functions

Abstract

The classical $abc$ theorem for polynomials (often called Mason's theorem) deals with nontrivial polynomial solutions to the equation $a+b=c$. It provides a lower bound for the number of distinct zeros of the polynomial $abc$ in terms of $\deg{a}$, $\deg{b}$, and $\deg{c}$. We prove some "local" $abc$-type theorems for general analytic functions living on a reasonable bounded domain $\Omega\subset\mathbb C$, rather than on the whole of $\mathbb C$. The estimates obtained are sharp, for any $\Omega$, and they imply (a generalization of) the original "global" $abc$ theorem by a limiting argument.