The participant must close out a failure to deliver for a short sale transaction by no later than the beginning of regular trading hours on the settlement day following the settlement date, referred to as T+4. If a participant has a failure to deliver that the participant can demonstrate on its books and records resulted from a long sale, or that is attributable to bona fide market making activities, the participant must close out the failure to deliver by no later than the beginning of regular trading hours on the third consecutive settlement day following the settlement date, referred to as T+6. If the position is not closed out, the broker or dealer and any broker or dealer for which it clears transactions (for example, an introducing broker)[9] may not effect further short sales in that security without borrowing or entering into a bona fide agreement to borrow the security (known as the “pre-borrowing” requirement) until the broker or dealer purchases shares to close out the position and the purchase clears and settles. In addition, Rule 203(b)(3) of Regulation SHO requires that participants of a registered clearing agency must immediately purchase shares to close out failures to deliver in securities with large and persistent failures to deliver, referred to as “threshold securities,” if the failures to deliver persist for 13 consecutive settlement days.[10]