fast_insert(Object elem) Returns a new set that contains all the elements of this and
also the given argument, assuming the argument is not in the set.
public boolean
has(Object elem) Is the argument "==" to one of the
objects in theSet.
Returns a new set that contains all the elements of this and
also the given argument, assuming the argument is not in the set.
See Also:JMLObjectSet.insert(Object)