Corralled

Yesterday, I started reading an old book that had been sitting on the shelf: Anatoly Karpov and Aleksandr Roshal, Anatoly Karpov: Chess is My Life, trans. Kenneth P. Neat (1980). The book contains two of Karpov's games from the Masters vs. Candidates, Leningrad 1966. In the first of these, Alexander Chistiakov managed to get his knight trapped on a7.

White to move

Chistiakov played 28.e4, losing the knight to a simple fork. I wondered why he did not play 28.Nb5. It did not take long to find the refutation.