(progn
  (bt:make-thread (lambda ()
    (with-open-file (s1 "/dev/tty" :direction :output :if-exists :append)
      (dotimes (i 50) (print i s1) (finish-output s1) (sleep .1)))))
  (bt:make-thread (lambda ()
    (with-open-file (s1 "/dev/tty" :direction :output :if-exists :append)
       (dotimes (i 50) (print i s1) (finish-output s1) (sleep .1))))))