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Re: bignums are bogus

You could always take the approach that Xerox did.  Implement bignums
in such an inefficient way that processing time grows to unacceptable
levels before representation limits are anything close to reached!

(Actually I only see a few possibilities for representation: a list of
fragments [Xerox uses lists of 14 bit components]; arrays of
fragments; or something your hardware supports which is sort of large:
e.g. 128 bit floating or 31 digit packed decimal on IBM 370s, 99 digit
decimal on Symbol-IIR, etc.  The first two could be expected to
support a million bits on almost anything from an IBM PC upwards. 
Operation time and "consing" overhead would be pretty grim.  Only the
array case might have an obvious hard upper bound.  The third case
would certainly verge on "broken" by almost any reasonable standards.