InChI=1/C13H11NO4/c1-8(15)14-11-6-4-3-5-9(11)10(13(14)17)7-12(16)18-2/h3-7H,1-2H3/b10-7 acetic acid, (1-acetyl-1,2-dihydro-2-oxo-3H-indol-3-ylidene)-, methyl ester, (2E)- methyl (2E)-(1-acetyl-2-oxo-1,2-dihydro-3H-indol-3-ylidene)acetate