Thank you for confirming 39a, I was already about 99% sure but always require assurance.
15 I had art = agency, possibly re/on for with reference to, but stumped at the 'au' completely and no clue how anything might add up to an answer would be interested if anyone's got a concrete solution as well.
It's not a term I've come across due to a very very minimal knowledge of art, so thank you for very much for getting me over the final hurdle!