code: public static final <S, E> Functional<S> functionalSet(Set<E> set) {
  		return new FunctionalSet<S, E>(set);
  	}
docs: Returns a functional wrapper for the input set, providing a way to apply
  a function on all its elements in a functional style.
  
  @param set
  the set to which the functor will be applied.
  @return
  a set that also extends this abstract class.