Problem calculating an expression with roots

[parisse]

I follow the same convention as maple for (-8)^(1/3), it seems mathematica too. I did not know maxima does not follow that convention, that's strange, I find it is more natural to have a definition that extends to the complex domain like for the logarithm (i.e. continuous for Im(z)>=0).
And you can use surd/NTHROOT if you prefer the real root.