Main motif of this puzzle: Opera mate
In opera mate, a rook checkmates the king. The rook is next to the king, but can't be captured, because it is protected by a bishop (or a queen on the diagonal), which also prevents the escape.
Learn more in this guide.
The hint button is in beta test. We recommend to use the button only after you've thought about the puzzle for some time without finding any idea.
Read more about the hint button in this blog post.