;; Solution to 3c

(defun rotate-3 (alist n)
  (append (nthcdr n alist)
          (butlast alist (- (length alist) n))
  )
)

;; Solution to 3b

(defun rotate-2 (alist n)
  (if (= n 0)
    alist
    (rotate-2 (append (rest alist) (list (first alist))) (- n 1))
  )
)

;; Solution to 3a

(defun rotate-left-by-n (alist n)
  (dotimes (i (mod n (length alist)) alist)
    (setf alist (append (rest alist) (list (first alist))))
  ) 
)

;; Solution to 2

(defun identity-p (amatrix)
  (let
    (
     (result t)
    )

    (dotimes (i (array-dimension amatrix 0) result)     
      (dotimes (j (array-dimension amatrix 0))
        (if (= i j)
          (if (not (= (aref amatrix i j) 1))
            (setf result nil)
          )
          (if (not (= (aref amatrix i j) 0))
            (setf result nil)
          )
        )
      )
    )
  )
)