HONG KONG (AP) — Shares of CXMT, China's largest memory chipmaker, shot skyward Monday as they began trading in Shanghai in mainland China’s biggest initial public stock offering in recent years. CXMT's shares surged 466% in their first day of trading. The company has become the most valuable one listed on a mainland Chinese exchange, with an estimated market capitalization of about 3. 3 trillion yuan (more than $487 billion). But that's still smaller than those of South Korean and memory...