Hi and thanks as always for cdb.

Please consider the following definition of an "inner product":

```
{α, β}::Indices(spacetime).
σ::LaTeXForm("\mathbf{σ}").
σ::DifferentialForm(degree=1).
e_{idx?}::LaTeXForm("\mathbf{e}", "_{", idx?, "}").
inner{a?? b??}::LaTeXForm("\langle",a??,", ",b??,"\rangle").
```

This works nicely when I write

`σβ := inner{σ e_{β}} ;`

but it fails when I write

`σβ := σ_{β} = inner{σ e_{β}} ;`

The error is

`RuntimeError: Free indices on lhs and rhs do not match`

What am I doing wrong please?

Thank you

GPN