Continent world ultimately persisted with these being regarded as separate continents. From the late 18th century, some geographers started to regard North America and South America as two parts of the world, making five parts in total. Overall though, the fourfold division prevailed well into the 19th century. Europeans discovered Australia in 1606, but for some time it was taken as part of Asia. By the late 18th century, some geographers considered it a continent in its own right, making it the sixth (or fifth for those still taking America as a single continent). In 1813, Samuel Butler wrote of Australia
Smallest-circle problem on "N". The algorithm is recursive, and takes as arguments two (finite) sets of points and ; it computes the smallest enclosing circle of the union of and , as long as every point of is one of the boundary points of the eventual smallest enclosing circle. Thus, the original smallest enclosing circle problem can be solved by calling the algorithm with equal to the set of points to be enclosed and equal to the empty set; as the algorithm calls itself recursively, it will enlarge the set passed into the recursive calls until it includes all the boundary points