(setf arr1 (make-array '(3) :initial-contents '(1 2 3)))
(setf arr2 (make-array '(3) :initial-contents '(4 5 6)))
(setf arr3 (make-array '(3) :initial-contents '(7 8 9)))
(setf arr4 (make-array '(6)))
(setf arr5 (make-array '(9)))
(setf arr4 (concatenate `(vector ,(array-element-type arr1)) arr1 arr2))
(format t "~a" "concatenate arr1 and arr2: ")
(write arr4)
(terpri)
(setf arr5 (concatenate `(vector ,(array-element-type arr1)) arr4 arr3))
(format t "~a" "concatenate arr4 and arr3: ")
(write arr5)
(terpri)