[kscarlet]

  (defparameter *a* '(1 2 3))
  (setf (car *a*) 3)

And this is undefined behavior because it mutates literal constant. I stopped reading further. The CL column is so bad.

[vindarel]

The trap is using quote, with the list operator there are no issues:

    (defparameter *a* (list 1 2 3))

and of course, mutating top-level variables is bad style.