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INF vs 1/0

Basically, reading and writing these guys either way is no big deal.
There are representations of infinity in several floating point formats
(IEEE single, double, extended), which are printed as #[s INF] etc.
in the simple read/print package I have.  #[r INF] would be consistent,
though eliminating some of the syntax  (the CL manual does not have the
[] stuff) may make numeric type info hard to determine.  I do not like
to use unbounded lookahead scanners.  (Think about reading an atom which
looks like a 2000 digit bignum, but then turns out to be something else
on the 2001th character).

Undefined numeric objects  ("Not A Number") in the IEEE stuff, is much
stickier.  Presumably there is some information encoded in the number
that should be presented (e.g. how the object was produced.)