[no subject]

[KMP at MIT-MC (Kent M. Pitman)]

The value of SETF must be its second arg. There is a ton of code by now
that depends on this, I'm sure. We want to be able to do something similar
to:

	(SUBST '(CAR X) 'A (SUBST 'SETF 'SETQ random-expression))

This is perhaps an oversimplification, but it shows a situation where it's
more useful to rely on a value related to the meta-notion of setting rather
than a value related to the operation-specific notion of RPLACA.