3H-Indol-3-one, 4-chloro-2-(4-chloro-1,3-dihydro-3-oxo-2H-indol-2-ylidene)-1,2-dihydro- 4,4'-Dichloroindigo 6275-44-1 C.I. 73025 Janson Indigo NSC33451 [.DELTA.2,2'-Biindoline]-3,3'-dione, 4,4'-dichloro-