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The truth value returned by predicates

It seems to me that, except for those predicates like MEMBER which return a
specific value, the implementation should be allowed to return any handy
non-false value.  This is inconsequential for microcoded implementations,
but could save a great deal in "stock hardware" versions.  Whether or not
more predicates should return useful values, as Stallman suggests, is a
different matter.  My feeling is "why not?" since programmers are free to
use this feature or not, as they see fit.  I think that it might lead to
obscure code, but I wouldn't force my opinion on others if it doesn't
infringe on me.  For the same reason, I think either option 1 or 2 for
NIL/() is reasonable.  In fact, most opinions on this matter seem to be "I
prefer X but I can live with Y."  Although I think () is cleaner, I'm
inclined to agree with Hedrick that it's not that much cleaner.  It truly
pains me to go for the conservative option, but I just don't think there's
enough to gain by changing.