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    Date: 31 AUG 1978 0549-EDT
    From: GLS at MIT-MC (Guy L. Steele, Jr.)
    To: RWK at MIT-MC, KGK at MIT-MC, (BUG LISP) at MIT-MC

        Date: 29 AUG 1978 2034-EDT
        From: RWK,KGK at MIT-MC
        Sent-by: RWK at MIT-MC
        To: (BUG LISP) at MIT-MC
        CC: RWK at MIT-MC, KGK at MIT-MC

        (SETQ POLY-1 '(NIL NIL 5 . 6))
        (SETQ POLY-2 '(nil nil nil nil))
        (APPEND POLY-1 POLY-2)
        MPV;APP1>>HLRZ A,(AR2A)

        Please fix to either work or give an error.
    PDP-10 MacLISP simply does not pretend to check for atoms other than
    NIL (sorry, ()) at the end of a list, because the atom test
    is too expensive in important inner loops like APPEND.
Mumble.  I would agree with that philosophy in compiled code.  However, it
makes it VERY difficult to do tutoring as to what a bug was, when the
entire LISP dies due to the user bug.  The normal mode of operation is that
the interpreter is used for interactive trials and debugging and similar
things.  For those purposes, you want to detect errors.  Otherwise the
code would be compiled!