| http://www.w3.org/ns/prov#value | - General formula: ##STR3## wherein any one of R1, R2, R3 and R4 is an aryl group or an aralkyl group and the others are a hydrogen atom or an alkyl group, respectively; n is an integer from 0 to 3; and when R4 is an aryl group or an aralkyl group, n is 1.
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