Stocks opened higher, but quickly turned mixed early Tuesday. The Dow Jones industrial average and the S&P 500 each edged up 0.1%. But the Nasdaq fell 0.2% after giving up a 0.2% gain in the stock market today. In economic news, the ISM service index fell to 56.2 in December from 59.3 in November. Views were for a reading of 58. Factory orders fell 0.7% in November, slightly worse than views for a 0.6% drop.