Every finite set of points with Span has an enclosing Circle with Radius no greater than .
References
Le Lionnais, F. Les nombres remarquables. Paris: Hermann, p. 28, 1983.
Rademacher, H. and Toeplitz, O. The Enjoyment of Mathematics: Selections from Mathematics for the Amateur.
Princeton, NJ: Princeton University Press, pp. 103-110, 1957.