1 (defun unique-triples (n)
2   "Unique triples of numbers <= n"
3   (flatmap
4    (lambda (i)
5      (flatmap
6       (lambda (j)
7 	(mapcar
8 	 (lambda (k) (list i j k))
9 	 (enumerate-interval 1 (1- j))))
10       (enumerate-interval 1 (1- i))))
11    (enumerate-interval 1 n)))
12 
13 (defune triples-sum-s (s n)
14   "Triples of numbers <= n summing to s"
15   (filter
16    (lambda (triple)
17      (= (sum triple) s))
18    (unique-triples n)))