Black to move
Two moves occurred to me and I examined both. As it turns out, my two candidate moves are the engine's top choices. After some thought, I selected the second best move. Tigran Petrosian selected the best move and went on to win.
*This position is number 28. John Dill brought Cheng's book to my attention last Wednesday as described in "A Zugzwang Lesson". Cheng's book contains tactics and positional exercises that span all phases of the game--opening, middle, ending. Some solutions are defensive in nature; others offensive. They are neither sequenced by theme, nor by difficulty. Many originate in games between amateurs.