| http://www.w3.org/ns/prov#value | - When this derivative is in the form of the pyridilium salt, it e.g. complies with the formula: ##STR9## in which R2 has the meaning given hereinbefore, R7 is a C1 to C4 alkyl radical, A is an anion chosen from among CL-, Br- and I- and M is a metal.
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