Regs might have seen this one before. I haven't read the sticky so I hope this is okay, apologies if not.
It's white to move, mate in 6 moves, I looked for over an hour and half, before giving up and checking answer, I also ran it through CM 10th edition which got mate in 8 moves against itself. See if you can get both.
Credit - by Giegold 1976
Regards Mack