Some operations create new values. Others extract values from values. Yet others modify values. Finally, there are also basic operations for determining to which class a piece of data belongs. Built-in operations and functions are of course just another class of data.
Definition is value creation, application is a form of value extraction.
When we define a function, we combine basic data operations. The former means that the result of one function becomes the argument of another one. The latter represents a choice among several possibilities. When we eventually apply a function, we trigger a computation. In this book we have studied the laws of basic operations and the laws of operation combination.