user7051: Why does Fritz prefer underpromotion in this position? How can underpromotion to bishop evaluate so much higher than normal queen promotion?
Can this be a bug in the Fritz 14 chess engine?


user1485: It's because 1. exf8=Q+ Kxh7 2. Rxd7?? would be stalemate. I think it is a even a theoretical draw after 1. exf8=Q+ Kxh7 2. Qg7+. Therefore 1. exf8=B+! (with check!) is better, since white then can keep an extra piece and win easily.
[FEN "5r2/3qPbkB/8/7P/8/8/8/1K1R4 w - - 0 1"]

1. exf8=Q+ (1. exf8=B+!) Kxh7 2. Rxd7? (2. Qg7+)


7051: <p>Why does Fritz prefer underpromotion in this position? How can underpromotion to bishop evaluate so much higher than normal queen promotion?</p>

<p>Can this be a bug in the Fritz 14 chess engine?</p>

<p><img src="https://i.stack.imgur.com/0O8db.png" alt="Strange evaluation"></p>
 1485: <p>It's because <code>1. exf8=Q+ Kxh7 2. Rxd7??</code> would be stalemate. I think it is a even a theoretical draw after <code>1. exf8=Q+ Kxh7 2. Qg7+</code>. Therefore <code>1. exf8=B+!</code> (with check!) is better, since white then can keep an extra piece and win easily.</p>

<pre><code>[FEN "5r2/3qPbkB/8/7P/8/8/8/1K1R4 w - - 0 1"]

1. exf8=Q+ (1. exf8=B+!) Kxh7 2. Rxd7? (2. Qg7+)
</code></pre>
