TOKYO (AP) — Shares soared Tuesday in Shanghai as Chinese markets reopened after a weeklong holiday but then gave up a chunk of their initial gains as officials in Beijing outlined details of plans to revive the world's second-largest economy. The Shanghai Composite index was up 5.5% at 3,519.88 and in Shenzhen, Japan's smaller market, the main index gained 5.3%. The Shanghai benchmark initially gained 10% but fell back as officials of China's main economic planning agency briefed reporters about a slew of policies announced earlier meant to address key problems such as a property market slump.