Thread: Why put the prototype inside the function definition?

The following is part of the code found on page 110 in the book "The C Programming Language" by K & R.

Code:

void qsort(char *v[], int left, int right)
{
     int i, last;
     void swap(char *v[], int i, int j);

     /*rest of the code*/
}

What's the reasoning for having the prototype for swap() inside the function definition of qsort()? Ie, why isn't the prototype for swap() before main()?