>You'll need to check against both 1/0 and -1/0 (don't know if there are any other specific NaN values we'd need to check). Of course as Thomas suggests, one could use the ABS() function to convert the negative NaN to a positive one.

I don't think there's a difference in fox... at least I didn't, but:

x=1/0
?x=1/0 && .t.
?x=-1/0   && .f.
?-x=-1/0  && .t.

shows that there is. However,

x=1/0
INSERT INTO zz VALUES (-10/0)
?x=num    && .t.

shows that in a field, only abs(nn/0) is stored

And I thought you were joking when you mentioned negative all-stars values.