5-Thia-1-azabicyclo(4.2.0)oct-2-ene-2-carboxylic acid, 7-(((4-(2-amino-1-carboxy-2-oxoethylidene)-1,3-dithietan-2-yl)carbonyl)amino)-7-methoxy-3-(((1-methyl-1H-tetrazol-5-yl)thio)methyl)-8-oxo-, Disodium Salt,(6R-(6alpha,7alpha))-