Limit Sets for Schottky Groups
A Schottky group is a special sort of Kleinian group, first studied by Friedrich Schottky in 1877.
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 D. Wright, "Indra's Pearls," Oklahoma State University. (Jan 13, 2021) klein.math.okstate.edu/IndrasPearls.
 A. Marden, "Book Review: Indra’s Pearls: The Vision of Felix Klein," Notices of the American Mathematical Society, 50(1), 2003 pp. 38–44. www.ams.org/notices/200301/rev-marden.pdf.