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re: It's a little more complicated (as if we needed that :-).  IEEE
    underflow traps don't happen for addition or subtraction, just for
    multiplication and division.  . . . 

What kind of hardware device are you describing?  The MC68881 will always
give you the traps you enable, regardless of the operation. [In fact, the
present query was prompted by our noticeing that the underflow traps occur
when a denormalized result is produced -- not merely when the number is
too small to be represented at all].  Maybe you are overlooking the fact 
that adding one normalized number and one unnormalized one isn't by itself 
trappable -- only if the result is subsequently denormalized will the trap 

re: Oh, yeah.  In answer to your original question, we don't care or use
    them for anything.  But a customer complained, so we changed to conform
    to the letter of CLtL.

Could you find out how "independent" that customer complaint is?  I know
that at least one other Common Lisp product changed its view on this matter
solely because Lucid's test suite complained about it.  It would be "no
information" if the customer who complained to Symbolics did so only because
he found a different resolution of the problem in Lucid Common lisp.

Bob Mathis has some knowledge of how this issue was resolved in the ADA
world.  How about it Bob? any clues?

-- JonL --