Is it permissible for a traveler to shorten the prayer (qasr) if they intend to stay for only four days, knowing that you mentioned in one place that the limit for shortening is twenty prayers, and in another place you mentioned it is three days?

Some jurists are of the opinion that the limit for praying in full is twenty prayers, while others hold it to be twenty-one prayers. Accordingly, whoever knows that he will stay for four full days, excluding the days of arrival and departure, should pray in full and not shorten his prayers. However, if the days of arrival and departure are included within these four days, then there is no blame upon him if he shortens his prayers.