| http://www.w3.org/ns/prov#value | - s of the formula ##STR14## in which R1 is a hydrogen atom, a carboxyl group or an alkyl, phenyl, nitrophenyl, dinitrophenyl, carboxyl-substituted phenyl or trialkylammoniumphenyl radical, R2 is a phenyl, nitrophenyl, biphenylyl or naphthyl radical, R3 is a phenyl, carboxyl-substituted phenyl, carboxyl-substituted hydroxyphenyl or dimethylthiazolyl radical, and A??? is a monovalent anion, which tet
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