Complex arc tangent

[Guy Steele <godot!gls@AQUINAS>]

I spoke with Paul Penfield yesterday, and he says that he now agrees
with Kahan on the treatment of the branch cut for complex arc tangent.
He proposes to write some sort of joint letter recommending to the APL
and Common Lisp communities that this Kahan's definition of the branch
cut be adopted.  This would mean a (small) change to Common Lisp if
we endorse it.  Then everyone who cares at all about complex functions
in IEEE arithmetic will agree on the branch cuts.  Are there any objections?
--Guy