Date: 30 Mar 87 09:35:33 EST
    From: primerd!DOUG@ENX.Prime.PDN
    How can one handle circular lists indescriminately in sequence
    functions? It seems to me that at minimum the function must record or
    mark each cons to avoid a recursive loop.   Am I missing an obvious point?
The technique is described in the form of a piece of code for
LIST-LENGTH on page 265 of CLTL.
--Guy