Two-circle theorem of flow in porous media (Q1821664)

In \textit{V. M. Radygin} and \textit{A. V. Kopaev}, The two-circle theorem [in: Motion of soluble impurities in flows through porous media, Tula (1983) on pp. 52-55], using the method of conformal mapping, an attempt was made to extend the known circle theorem of flow in porous media to the case of two circular regions of the same radius occupied by the same medium. Using bipolar coordinates, the theorem is further extended to cover the problem of circular inclusions of different radii and different permeabilities. A corresponding theorem for two contiguous inclusions is presented as a limiting case. The exposition is illustrated with examples from which the results described in the literature follow as special cases.