>>> "ESF" == Eric S Fraga <e.fraga@ucl.ac.uk> writes:

> On Monday, 14 Dec 2020 at 10:19, Uwe Brauer wrote:
>> Consider please the following example 

> [...]

>> It should be exported as
>> 
>> \author{Uwe Brauer}

> It does for me.

Ok I had set 
org-export-with-author to nil
now I set it to t and the export works, 

*however* set to t it *always* exports, setting to nil it *never*
 exports.

I would like that it only exports if the field 
#+AUTHOR is present.

This seems to be impossible the documentation states

Documentation:
Non-nil means insert author name into the exported file.
This option can also be set with the OPTIONS keyword,
e.g. "author:nil".

But it is not clear how to set this 

I tried 
#+TITLE: This title
#+AUTHOR:
:PROPERTIES:
:AUTHOR:nil
:END:

But this did not work as expected.

>> and the dynamic effect as 

> Use BEAMER_act instead of BEAMER_opt and specify the property as [<+->],
> i.e. with square brackets.

Thanks, this was helpful