NMAP a good idea.

["Scott E. Fahlman" <Fahlman@C.CS.CMU.EDU>]

Just so that your message will not cause a flood of bug reports to
Common Lisp implementors:

It has not been established that it is a bug for sequence functions not
to handle circular lists.  There seems to be strong sentiment on both
sides of this issue, and there is no clear statement on this in the
manual.  At some point the standardization committee will have to make a
decision one way or the other.

If it were up to me (which it isn't) it would be an error to pass a
circular list to any function that does not explicitly allow circular
lists.  I don't think the extra cost of handling this style is justified
for most functions.  Sequences should be finite.

-- Scott