41.   Stock index futures, unlike stocks, trade for most of the night.

42.   Stock investors can use index futures to hedge themselves against the risk of sharp price swings, or to speculate on the possibility that prices will rise or decline.

43.   Such selling drove down the prices of stock index futures and brought in index arbitragers, who bought the futures and then sold individual stocks.

44.   Stock index futures traders at the Chicago Mercantile Exchange said that sparked selling in the bond market, which spilled over to stock futures.

45.   Stock index futures allow investors to speculate in the general direction of an industry, or hedge against declines.

46.   Telebras options expire on Monday and Bovespa index futures expire tomorrow.

47.   That had led to some money managers selling stock index futures, a tactic that would have protected them in the event of a market decline.

48.   That rule bars certain trades by those who arbitrage the prices of stock index futures and the actual stocks.

49.   The advent of stock index futures provided a way to hedge risk on broad baskets of stocks.

50.   The drop initially was exacerbated by the quarterly expiration of stock index futures, options on those futures and common stock options.