Hi Luca and Kasper.

I was puzzled by your post Luca, and wanted to try myself. FYI I'm using a fair new version of cadabra (`Version 2.3.9 (build 2829.40f334a67c dated 2022-08-05)`

).

## Your code

First let me point that I copy your code and my cadabra session got stocked! Weird, because so far you're defining a expression.

**Problem:** there is a `\+`

in your `ex`

.
**Solution:** Change `\+`

by `+`

.

Then, unlike Kasper, *I reproduce your error!* Even more puzzled...

Since you're not computing anything (yet), I tried the rendering.

**Possible problem:** Rendering options.
**Solution:** simplifying the rendering properties.

Then, I got the expected result.

## Updated code

**NOTE:** I've added the algorithms suggested by Kasper

```
{\alpha,\beta,\gamma,\delta,\alpha#,\beta#}::Indices(spinor, position=fixed).
{a,b,c,d,e,a#, b#}::Indices(flat,position=fixed).
\gamma{#}::GammaMatrix(metric=\eta);
\delta{#}::KroneckerDelta.
{\psi1, \psi2}::Spinor(dimension=4, type=Majorana);
\bar{#}::DiracBar.
# {\psi1, \psi2}::AntiCommuting.
# {\psi1, \psi2}::SortOrder.
# \psi1::LaTeXForm("\psi_{1}").
# \psi2::LaTeXForm("\psi_{2}").
ex:= \bar{\psi1} \gamma_{a b} \gamma_{c} \psi2 + \bar{\psi2} \gamma_{a b} \gamma_{c} \psi1;
join_gamma(_)
distribute(_)
sort_spinors(_);
```

See the result in an image

# UPDATE 1

Sorry I noticed that I commented a couple of desired properties...

## The new code

```
{\alpha,\beta,\gamma,\delta,\alpha#,\beta#}::Indices(spinor, position=fixed).
{a,b,c,d,e,a#, b#}::Indices(flat,position=fixed).
\gamma{#}::GammaMatrix(metric=\eta);
\delta{#}::KroneckerDelta.
{\psi1, \psi2}::Spinor(dimension=4, type=Majorana);
\bar{#}::DiracBar.
{\psi1, \psi2}::AntiCommuting.
{\psi1, \psi2}::SortOrder.
# \psi1::LaTeXForm("\psi_{1}").
# \psi2::LaTeXForm("\psi_{2}").
ex:= \bar{\psi1} \gamma_{a b} \gamma_{c} \psi2 + \bar{\psi2} \gamma_{a b} \gamma_{c} \psi1;
join_gamma(_)
distribute(_)
sort_spinors(_);
```

See the new result