| http://www.w3.org/ns/prov#value | - wherein each of R19, R20, and R21 independently represents a hydrogen atom, a lower alkyl group having 1 to 8, preferably 1 to 4 carbon atoms, or a halogen atom, such as chlorine, fluorine, or bromine; and p is an integer of 1 to 12, preferably 1 to 8, and more preferably 1 to 4.
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