At the stock markets, after a firm opening, the Sensex at the Bombay Stock Exchange gave up all its initial gains, and after swinging between positive and negative territory, advanced a marginal 20 points to 31,242, a short while ago.The Nifty at the National Stock Exchange added 12 points to 9,627.And at the foreign exchange market, the rupee appreciated 11 paise to 64 rupees 77 paise against the dollar in afternoon deals.