(defun flotri (n)
  (let* ((last (trunc (* n (+ n 1)) 2))
         (colw (mapcar [chain tostring length]
                       (range (- last n -1) last)))
         (x 0))
    (each ((r (range* 0 n)))
      (each ((c (range 0 r)))
        (format t " ~*a" [colw c] (inc x)))
      (put-line))))

(defun usage (msg)
  (put-line `error: @msg`)
  (put-line `usage:\n@(ldiff *full-args* *args*) <smallish-positive-integer>`)
  (exit 1))

(tree-case *args*
  ((num blah . etc) (usage "too many arguments"))
  ((num) (flotri (int-str num)))
  (() (usage "need an argument")))