The concept of a function is one of the most useful abstractions in mathematics. In fact, it is an abstraction that can be further abstracted! For instance, an operator is an entity which takes functi...The concept of a function is one of the most useful abstractions in mathematics. In fact, it is an abstraction that can be further abstracted! For instance, an operator is an entity which takes functions as inputs and produces functions as outputs, thus an operator is to functions as functions themselves are to numbers. There are many operators that you have certainly encountered already – just not by that name.
