Hungarian publication unknown artist set up (6)
I believe the answer is:
Here is my best explanation:
'hungarian' is the definition.
('Magyar' can be a synonym of 'hungarian')
'publication unknown artist set up' is the subsidiary indication.
'publication' becomes 'mag' (abbreviation for magazine).
'unknown' becomes 'y' (algebra).
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'set up' is a reversal indicator.
'ra' backwards is 'ar'.
(Other definitions for magyar that I've seen before include "European", "Hungarian language" and "Official language of Hungary".)