Balayage of measures and subharmonic functions on a system of rays. I. Classic case

We develop classical balayage (sweeping) measures and subharmonic functions on the ray system $S$ with a general origin on the complex plane $\mathbb C$. This allows for a subharmonic function $v$ on $\mathbb C$ to construct also a subharmonic function on $\mathbb C$ that is harmonic outside $S$ and coincides with $v$ on $S$. We give applications to the relationship between the growth of an entire function on $S$ and the distribution of its zeros, the conditions of complete regular growth of entire and subharmonic functions on the ray system, to the problems of incompleteness of exponential systems in the spaces of holomorphic functions in nonconvex unbounded open sets narrowing near infinity. This first part of our work contains the necessary preparatory material for the construction of a new type of finite genus balayage on $S$ in the second part.