Erasing all its early gains, the Sensex at the Bombay Stock Exchange fell 89 points, or 0.4 percent, to 20,787, in afternoon trade, a short while ago, on profit-booking by investors, and amid some mixed quarterly corporate results. Earlier in the morning, the Sensex had opened 60 points higher, at 20,936.Other Asian markets in Japan, China, Hong Kong, and Singapore rose between 0.3 percent and 1.8 percent, as higher oil and metal prices boosted commodity stocks, and as President Obama called on world leaders at the Group of 20 summit to work together to advance economic recovery.