[Axiom-developer] differences

[daly]

As far as I know so far Axiom just uses the underlying lisp values
from cos and acos.

I don't consider it a bug but I don't consider it "stable" either.
All other values of all other functions seem to give the same
result and that result matches the input in this case. It's a 
curious result though. I'd expect that they are using Chebyshev
polynomials and I'd have expected a symmetric result. Somebody
clearly "optimized" the world by saving an instruction somewhere.

The problem arose trying to explain a failing case in the
regression tests. Now that I understand it better it's not an issue.

Tim