The append Function

The append function attaches one list to another. Thus,

(append '(1 2 3 4) '(5 6 7 8))

produces the list

(1 2 3 4 5 6 7 8)

This is exactly how we want to attach two lengths’ lists produced by lengths-list-file to each other. The results contrast with cons,

(cons '(1 2 3 4) '(5 6 7 8))

which constructs a new list in which the first argument to cons becomes the first element of the new list:

((1 2 3 4) 5 6 7 8)