| http://www.w3.org/ns/prov#value | - R may, and preferably will, include one or moreheteroatoms via one or more divalent internal linking groups such as esters, amides, secondary carbamates, ethers, secondary ureas, ketones, and mixtures thereof.Preferred R groups are H, --CH.sub.3, aromatic groups such as benzyl, and alkyl esters of from 2 to 10 carbons, especially from 4 to 8 carbons.
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