2-Pyrone-4,6-dicarboxylic acid 2-oxo-2H-pyran-4,6-dicarboxylic acid 2H-pyran-4,6-dicarboxylic acid, 2-oxo- 6-Oxo-6H-pyran-2,4-dicarboxylic acid InChI=1/C7H4O6/c8-5-2-3(6(9)10)1-4(13-5)7(11)12/h1-2H,(H,9,10)(H,11,12