Check if a 2D Vector is a Magic Square

magic-squares.lisp

;;; Magic Squares - https://www.reddit.com/r/dailyprogrammer/comments/4dccix/20160404_challenge_261_easy_verifying_3x3_magic/

(defun magic-square? (square)
  (let* ((dims (array-dimensions square))
	 (size (car dims)))
    (if (and (typep square 'simple-array)
	     (eq 2 (array-rank square))
	     (eq size (cadr dims)))
	(loop for i from 0 below size
	   for j from 0 below size
	   summing (aref square i j) into lr
	   summing (aref square i (- size j 1)) into rl
	   finally (return (eq lr rl)))
	nil)))