Composing Functions, Revisited Again

In section~#secprogramfunctions#13853> we said that programs were collections of function definitions and possibly some variable definitions, too. To guide the division of labor among functions, we also introduced a rough guideline:
``Formulate auxiliary function definitions for every dependency between quantities in the problem statement.''
So far the guideline has been reasonably effective, but it is now time to take a second look at it and to formulate some additional guidance concerning auxiliary functions. In the first subsection, we refine our original guideline concerning auxiliary programs. The suggestions mostly put into words the experiences that we made with the exercises. The second and third one illustrate two of the ideas in more depth; the last one is an extended exercise.