“Thiol-thione tautomeric forms recognition on the example of 4-[3-(2- methyl-furan-3-yl)-5-thioxo-1,2,4-triazolin-4-yl]acetic acid” Agata Siwek, Monika Wujec, Irena Wawrzycka-Gorczyca, Piotr Paneth, Maria Dobosz, Heteroatom Chem. 19, 337-344 (2008)