1.   The decrease came as at least one type of trading collar that restricts program trading was triggered each day.

2.   The New York Stock Exchange imposed its trading collars a record four times today, as investors weathered the most volatile month for stocks in at least a year.

3.   The NYSE also imposes trading collars, which restrict some computer-driven trading.

4.   The trading collar was still in place at the close.

5.   These trading collars restrict index-arbitrage trading.