Hi! When I run the following code, Cadabra gives me
*ConsistencyException: Free indices in different terms in a sum do not match.*

```
{i,j,k}::Indices(vector);
N::Integer;
{i,j,k}::Integer(1..N);
_:= \nabla^{i}{v_{i}} - 2 \nabla_{i}{v^{i}} ;
canonicalise(_);
```

Is something wrong with the code? Substituting

` substitute(_, $\nabla^{i}{v_{i}} -> \nabla_{i}{v^{i}}$)`

did not help. Can I force Cadabra to combine the two terms in another way?

Many thanks! Andreas