>>>>> "Pedro" == Pedro Fortuny <P.Fortuny@qmw.ac.uk> writes:
Pedro> There is no algebraic difference between +I and -I, so one needs
Pedro> make no difference between them. ONLY WHEN one fixes a topological
Pedro> representation of $C$ as a plane (for example) and gives it an
Pedro> orientation, etc... one gets a "real" difference, but from the
Pedro> purely algebraic (and that is what a CAS does) point of view,
Pedro> one cannot (is not able to) make any difference between "the" two
Pedro> roots of x^2+1=0 over $R$. The fact could be stated as:
You mean $C$?
In any case I think the arg function is well-defined function (if we
use the principal value) and arg(%i) is %pi/2, but arg(-%i) = -%pi/2.
I think they're different, but perhaps I don't follow you.
Ray