Is it possible to cover completely the surface of a Sphere with congruent, nonoverlapping arcs of Great Circles? Conway and Croft (1964) proved that it can be covered with half-open arcs, but not with open arcs. They also showed that the Plane can be covered with congruent closed and half-open segments, but not with open ones.

**References**

Conway, J. H. and Croft, H. T. ``Covering a Sphere with Great-Circle Arcs.'' *Proc. Cambridge Phil. Soc.*
**60**, 787-900, 1964.

Gardner, M. ``Point Sets on the Sphere.'' Ch. 12 in *Knotted Doughnuts and Other Mathematical Entertainments.*
New York: W. H. Freeman, pp. 145-154, 1986.

© 1996-9

1999-05-26