Mumbai, Sept. 7 -- The stock market regulator may look to bring back the old mechanism to settle derivative contracts on expiry days, two people aware of the discussions said, in a partial revision to the closing auction session (CAS) introduced a month ago. The goal is to smooth out last-minute swings on settlement days, which open up gaps between the Nifty and Sensex. The Securities and Exchange Board of India (Sebi) on Thursday said it will review the settlement process after receiving market feedback and said it may issue a consultation paper on the matter within a week. According to the people cited above, while the daily CAS will continue as before, Sebi may propose settling weekly and monthly derivatives using the previous volume-wei...