Underpromotion Milestones – part 3

Finally, in this three-part series, we come to the first full Babson task endgame study, composed by Gady Costeff. Many thought it was not possible to fulfil this extremely difficult task. Harold van der Heijden describes the full story. But one problem remains: the position is not legal. Costeff had already constructed it in 2011 and tried in vain to find a legal version. So this is still an open problem. Maybe you can give it a try?