Leela recently won the TCEC Cup, a knockout competition of computer engines[1]. It's increasingly clear that it's a top 3/4 engine at this point, despite various setbacks and resets over the last year.<p>Quite apart from the chess side of things, there are many fascinating lessons to learn about how to manage and debug issues in these sorts of deep learning systems. For example, at one point there was a serious bug with underpromotion which affected millions of training games, and it was interesting to see debates about whether the system would just correct itself over time once that was fixed, or whether it would be permanently skewed.<p>[1] <a href="https://groups.google.com/forum/#!topic/lczero/3uI_dTa1Ksg" rel="nofollow">https://groups.google.com/forum/#!topic/lczero/3uI_dTa1Ksg</a>