LONDON: European and Asian stock markets mostly retreated on Wednesday (Apr 16) after the United States government imposed restrictions on exports of a key Nvidia chip to China, the latest trade war salvo between the world's biggest economies. Nvidia late on Tuesday notified regulators that it expects a US$5.5 billion hit this quarter owing to a new US licensing requirement on the chip it can legally sell in the Asian country. The company at the heart of helping to power artificial intelligence