code: public ImmutableRangeSet<C> difference(RangeSet<C> other) {
      RangeSet<C> copy = TreeRangeSet.create(this);
      copy.removeAll(other);
      return copyOf(copy);
    }
docs: Returns a new range set consisting of the difference of this range set and {@code other}.
  
  <p>This is essentially the same as {@code TreeRangeSet.create(this).removeAll(other)} except it
  returns an {@code ImmutableRangeSet}.
  
  @since 21.0