(defun split (P1 P2 P3)
(list (list P1
        (list (/ (+ (car P1) (car P2)) 2) (/ (+ (cadr P1) (cadr P2)) 2))
        (list (/ (+ (car P1) (car P3)) 2) (/ (+ (cadr P1) (cadr P3)) 2)))
      (list (list (/ (+ (car P1) (car P2)) 2) (/ (+ (cadr P1) (cadr P2)) 2))
        P2
        (list (/ (+ (car P2) (car P3)) 2) (/ (+ (cadr P2) (cadr P3)) 2)))
      (list (list (/ (+ (car P1) (car P3)) 2) (/ (+ (cadr P1) (cadr P3)) 2))
        (list (/ (+ (car P2) (car P3)) 2) (/ (+ (cadr P2) (cadr P3)) 2))
        P3)))

(defun calc (dreieck tiefe)
(cond ((= 0 tiefe) dreieck)
      (t (calc (loop for i in dreieck append (apply 'split i)) (- tiefe 1)))))

(defun draw_triangle (P1 P2 P3)
(format nil "~%<polygon points=\"~,30f,~,30f ~,30f,~,30f ~,30f,~,30f\" fill=\"#000000\"/>"
        (car P1) (cadr P1)
        (car P2) (cadr P2)
        (car P3) (cadr P3)))

(defun paint (L)
(loop for i in L collect (apply 'draw_triangle i)))

(defun build (name X Y dim)
(with-open-file (svg name :if-exists :supersede :direction :output)
(format svg "<svg xmlns=\"http://www.w3.org/2000/svg\" width=\"~Apx\" height=\"~Apx\">" X Y)
(format svg "~{~A~}" (paint (calc `(((5 ,(- Y 5)) (,(/ X 2) 5) (,(- X 5) ,(- Y 5)))) dim)))
(format svg "~%</svg>")))

(build "bild.svg" 1024 768 12)