Josip Plemelj solves the Riemann problem about the existence of a differential equation with a given monodromic group and uses Sokhotsky-Plemelj formulae.
↑Pasechnik, I. P. (1986). "Refinement of the moment of explosion of the Tunguska meteorite from the seismic data". Cosmic Matter and the Earth (in Russian). Novosibirsk: Nauka. p.66.