Mate in 5 Exercise 20

White plays and wins in 4 moves https://lichess.org/XZ7hnagZ

1. Be6 Ka8 2. Kb6 Kb8 3. Na6+ Ka8 4. Bd5#

The analysis board does checkmate in 5 moves

1. Be6 Ka7 2. Kc7 Ka8 3. Kb6 Kb8 4. Na6+ Ka8 5. Bd5#

Source:

https://www.amazon.com/Chess-Puzzles-Advanced-Expert-Level/dp/B0917YQZP1