LONDON/PARIS (Reuters) -The three co-founders of AllianceBernstein's Autonomous research unit have quit, ahead of the U.S. investment firm merging its equities business with French bank Societe Generale. Stuart Graham, a highly regarded banks analyst who joined AllianceBernstein in 2019 after it bought the financial sector-focused research firm he co-founded, is leaving in March to take a six-month break from work, he told Reuters. The other two co-founders of Autonomous, Ed Allchin and Manus Costello, are also leaving, Graham said in an email.