What is the point of an open mapping, I mean what are you trying to do when you have an open mapping really? This encyclopediaofmath.org/index.php/Open_mapping says you can interpret it as a form of continuity for the inverse of a many-valued mapping, what question/concept is an open mapping answering/addressing, and why is it not as random as defining a jugular as a map which maps every third open set to an open set?