The reference http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node128.html
is more clear than is CHLS about the continuity of atanh. Indeed,
atanh(-2) = -1.57....*%i - 0.54930...
In the long run, I think we should change rectform and logarc to
use atanh(x) = log((1+x) * sqrt(1/(1-x^2)), and etc. In the short
run, I don't know--GCL gets most of this stuff wrong. Some of
yesterday's modifications to trigi.lisp produce inaccurate values
for atanh for values near zero. I don't think that's something
we want to allow.
Barton