It seems that there is a bug in the string_states example: the third block of code defines $\delta$ as:

```
\delta{#}::KroneckerDelta.
\delta{#}::Diagonal.
```

but it seems that this directly sets any off-diagonal component to zero:

`X := \delta_{m}^{n};`

gives $0$.

By comparing with other notebooks or arxiv:1912.08839 it seems that the `Diagonal`

property should not be there. Is this correct?