Study by D. Petrov 1st prizewinner

This study formed part of a lecture by David Fredgood at a meeting of the British Chess Problem Society last week entitled 'Some favourite light weight studies', which I am told was very good. I had no idea how to solve it so a small clue is that it is included in a compilation by G.M. Kasparyan called 'Domination in 2,545 (!) Endgame Studies.