```
{% set admin = true %}

{% extends admin ? "AcmeAdminBundle::admin.html.twig" : "AcmeUserBundle::user.html.twig" %}

{% form_theme form _self %}

//custom stuff

<form action="{{ path('process_form')}}" method="post" {{ form_enctype(form) }}>
//...whatever
</form>

```

It looks like `{% form_theme form _self %}` removes global variables as I get the following error:
"`Variable "admin" does not exist`"

What should I do to extend the template properly in that case...?