真ん中優先。真ん中がないときは右側優先。
(define thin-out
(lambda (lis n)
(let* ((r (- (length lis) n))
(a (if (= (mod r 2) 0) (/ r 2) (+ (div r 2) 1)))
(b (+ a n)))
(append (take lis a) (drop lis b)))))
(print (iota 10))
(print (thin-out (iota 10) 1))
(print (thin-out (iota 10) 2))
(print (thin-out (iota 10) 3))
^o^ > gosh thin-out.scm (0 1 2 3 4 5 6 7 8 9) (0 1 2 3 4 6 7 8 9) (0 1 2 3 6 7 8 9) (0 1 2 3 7 8 9)