  A problem that is simple to state in the context of spherical geometry, and
that seems rather interesting, appears to have been unexamined to date in the
mathematical literature. The problem can also be recast as a problem in the
real projective plane. The problem on the sphere involves four great circles
and their intersections. A substantial claim is made concerning this problem,
and subsequently proved by relating the spherical problem to a compelling
problem in solid geometry. This latter problem essentially concerns
relationships between the angles of a tetrahedron, and has practical
applications, particularly in connection with the Perspective 3-Point (Pose)
Problem.
