[Sharlin]

Indeed, AFAIK neural networks have caused at least two AI winters before finally breaking through thanks to a few good new ideas and the fact that the needs of computer games incidentally led to the development of a big industry of specialized, programmable, high-performance dot product calculators.

[praptak]

Speaking of winters; there's a good article about Cyc, a successor to Automated Mathematician. Cyc was the last big project in symbolic AI: https://yuxi.ml/cyc