Building on early gains, the Sensex at the Bombay Stock Exchange shot up a massive 412 points, or 2.1 percent, to again cross the 20,000 mark, at 20,135 in afternoon trade, a short while ago. Earlier in the morning, the Sensex had opened with a gain of 158 points, or 0.8 per cent, at 19,880, on continued buying by funds and retail investors. The Sensex rose after wholesale price based inflation eased to an over three-year low, raising hopes of a rate cut by the Reserve Bank, and as regional markets climbed.Other Asian markets in Japan, China, South Korea, Hong Kong, Taiwan, Singapore and Indonesia had gained between 0.1 percent and 2.2 percent, today, with Japan's key stock index surging to a fresh 5-1/2 year high. Over on Wall Street, the US Dow Jones Industrial Average had ended 0.8 percent higher in yesterday's trade.