. "3-(5-Methyl-[1,3,4]thiadiazol-2-ylsulfanylmethyl)-8-oxo-7-(2-tetrazol-1-yl-acetylamino)-5-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid anion" . "19" . . . . .