# Pastebin x1pYASI8
COMMON-LISP-USER> (defparameter tree '#2=(#1=(a) (b c a #1# #2#) . #2#))
(setf *print-circles* t)
(print-identified-conses tree)

TREE
COMMON-LISP-USER> ;;; Warning:       Undefined variable *PRINT-CIRCLES*
;;;     at -unknown-file- filepos: 0  lineno: 0 
T
COMMON-LISP-USER> #1=(#2=(#3=A . ()) . ((B . (C . (#3#  . (#2#  . (#1#  . ()))))) . #1# ))
((A)
 (B C A (A)
  ((A)
   (B C A (A)
    ((A)
     (B C A (A)
      ((A)
       (B C A (A)
        ((A)
         (B C A (A)
          ((A)
           (B C A (A)
            ((A)
             (B C A (A)
              ((A)
               (B C A (A)
                ((A)
                 (B C A (A)
                  ((A)
                   (B C A (A)
                    ((A)
                     (B C A (A)
                      ((A)
                       (B C A (A)
                        ((A)
                         (B C A (A)
                          ((A)
                           (B C A (A)
                            ((A)
                             (B C A (A)
                              ((A)
                               (B C A (A)
                                ((A)
                                 (B C A (A)
                                  ((A)
                                   (B C A (A)
                                    ((A)
                                     (B C A (A)
                                      ((A)
                                       (B C A (A)