A Rex Solus direct mate problem is one where Black has no pieces apart from the king.
American problemist Steven Dowd has just started a Rex Solus group on Facebook to demonstrate problems of this nature.
This is a mate in 6 composed by Albert Grigoryan (StrateGems 2004).
Steven pointed out that moving the pawn on h2 to g2 produces a twin – also mate in 6, but with a completely different solution.
So you get two problems this week for the price of one.
Good luck in solving them!