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Ackman Fought to Keep SEC Rule That Enabled Allergan Deal

Pershing Square Capital Management LP owes its ability to amass an undetected stake of almost 10 percent in Allergan Inc. to a regulation it lobbied to preserve three years ago.

Pershing Square, the hedge-fund firm led by Bill Ackman, recruited a group of large investors in 2011 that persuaded the Securities and Exchange Commission to reconsider reducing a 10-day window that investors have to disclose stakes of five percent or more in a company. The SEC had successfully pushed for authority to shorten the reporting requirement in the 2010 Dodd-Frank Act.