1H-2-benzopyran-3,4-dicarboxylic acid, 1-oxo-, 4-methyl ester 4-(methoxycarbonyl)-1-oxo-1H-isochromene-3-carboxylic acid InChI=1/C12H8O6/c1-17-12(16)8-6-4-2-3-5-7(6)11(15)18-9(8)10(13)14/h2-5H,1H3,(H,13,14