Hiroshi Okumura and Masayuki Watanabe, Remarks on Woo's Archimedean circles,
Forum Geometricorum, 7 (2007) 125--128.

Abstract: The property of Woo's Archimedean circles does not hold only for Archimedean circles but circles with any radii. The exceptional case of this has a close connection to Archimedean circles.

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