I am doing some calculations on classical fields.

When expressions like $$k_i k_i k_\beta k_\beta$$ appear, I wish to simplify them using the assumption that $$k_i k_i = 1$$.

However, when I try do so the following way, the dummy index label seems to confuse Cadabra:

```
a:= k_i k_i k_{\beta} k_{\beta};
N:= k_i k_i = 1;
substitute(a,N);
```

Output:

$$k_\beta k_\beta$$

I am using the jupyter kernel installed via conda, on OSX. Is this the intended behaviour? Am I doing something wrong?