Is the pronoun "on" compulsory here?
I wonder that too
Me too-- my sentence was marked as being wrong without ON ar the beginning.
There are some accepted translations that do not place on at the beginning of the sentence. But we have no current report for such a sentence, so we can't see exactly what you wrote. Please use the Report button, even if you also comment.
Sorry-- my translation was: Ale neni odbornik!
Currently all accepted forms contain "on" somewhere but in this case it can be acceptable without it we were already talking about him. I will allow it.