Package Mapset implements a simple and generic set collection. Items stored
within it are unordered and unique. It supports typical set operations:
membership testing, intersection, union, difference, symmetric difference and
cloning.
Package Mapset provides two implementations of the Set interface. The default
implementation is safe for concurrent access, but a non-thread-safe
implementation is also provided for programs that can benefit from the slight
speed improvement and that can enforce mutual exclusion through other means.
