Input (grade 8): The shortest path from point A to point B on a sphere is given by the shorter arc of the great circle passing through A and B/O. If A and B are antipodal points (like the North pole and the South pole), then there are infinitely many shortest paths between them.
Output (grade 12): In a sphere two antipodal points (points opposite each other on a sphere such as the North Pole and South Pole on Earth) have an infinite number of such paths between them.