Find the plane lamina of least area
which is capable of covering any plane figure of unit generalized
diameter. A unit circle is too small, but a hexagon circumscribed on the unit
circle is larger than necessary. Pál (1920) showed that the hexagon can
be reduced by cutting off two isosceles triangles
on the corners of the hexagon which are tangent to the hexagon's incircle
(Wells 1991; left figure above). Sprague subsequently demonstrated that an additional
small curvilinear region could be removed (Wells 1991; right figure above). These
constructions give upper bounds.

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