 They marked questionable or corrupt words or passages in manuscripts of the Homeric epics.The system was further refined by his student Aristophanes of Byzantium, who first introduced the asterisk and used a symbol resembling a for an obelus; and finally by Aristophanes' student, in turn, Aristarchus, from whom they earned the name of "Aristarchian symbols".While the asterisk ("asteriscus") was used for corrective additions, the obelus was used for corrective deletions of invalid reconstructions.