Erasing all its early losses the, the Sensex at the Bombay Stock Exchange ended with a marginal gain of 23 points, or 0.2 percent, at 15,988, on Monday, on hopes of a rate cut by the Reserve Bank.The Nifty rose 7 points, or 0.1 percent, to 4,848.But, stock markets in Japan, China, Hong Kong, South Korea and Singapore slumped between 1.7 percent and 2.8 percent.