### Interface of maxima atensor with sage

I am trying to use the atensor module of maxima in sage. I have trouble understanding the meaning of the symbols. According to the manual the basis of the algebra is given by v[1], v[2] etc, and atensimp(v[1].v[1]) should give -1. But, when I try to reproduce the result, I get the following.

```
maxima('init_atensor(dirac)')
maxima('atensimp(v[1].v[1])')
atensimp(v[1]^^2)
```

I am trying to reproduce the algebra of gamma matrices

```
{gamma^mu,gamma^nu}=2 eta^{mu nu}
```

where {,} stands for anticommutator. and eta^{mu nu} is the metric.
as described here
http://en.wikipedia.org/wiki/Gamma_matrices