Op do 28 feb. 2019 om 08:51 schreef Cecil Westerhof <cldwesterhof@gmail.com
>:

> I can set a checkbox to intermediate with:
>     C-u C-u C-c C-x C-b
>
> But I want to do it with code. How would I do that?
>

Found it. Quit simple:
    (org-toggle-checkbox '(16))

-- 
Cecil Westerhof