code: public <R> Tuple4<T1, T2, R, T4> mapT3(Function<T3, R> mapper) {
  		return new Tuple4<>(t1, t2, mapper.apply(t3), t4);
  	}
docs: Map the 3rd part (T3) of this {@link Tuple4} into a different value and type,
  keeping the other parts.
  
  @param mapper the mapping {@link Function} for the T3 part
  @param <R> the new type for the T3 part
  @return a new {@link Tuple4} with a different T3 value