Calling a function is like giving it a hug with parentheses.
Functions are usually defined before they are used.
But they can also be defined inline.
Or using an even shorter syntax.
Even Anonymous functions may take multiple arguments.
One function can beget another.
One function can beget another.
Functions can also take other functions as input.
Higher-order functions take functions as arguments.
But they are often better written using the names of others.