“…In the literature, of course, it also is possible to see numerous scientific researches associating with certain special types constituted by some of earlier elementary differential operators (or, their implications / applications) that we have also defined just above. For some of them, there also is a need to call up some comprehensive information (or, reminders) (cf., e.g., [1,2,3,11,13,14,15]), as follows.…”