[1]> (setf x1 0)
0
[2]> (setf x2 1)
1
[3]> (setf y1 10)
10
[4]> (setf y2 15)
15
[5]> (defun square (x) (expt x 2))
SQUARE
[6]> (defun euclidean-distance (x y) (sqrt (apply '+ (mapcar 'square (mapcar '- x y)))))
EUCLIDEAN-DISTANCE
[7]> (euclidean-distance (list x1 x2) (list y1 y2))
17.20465
[8]> (bye)