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 ".equals" 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:JMLEqualsSet.insert(Object)