| http://www.w3.org/ns/prov#value | - ##STR00018## in which R.sub.29 represents a hydrogen atom, a CH.sub.3O, CH.sub.3CH.sub.2O or phenyl radical, R.sub.30 denotes hydrogen or a lower alkyl radical such as methyl or ethyl, R.sub.31 denotes hydrogen or a lower alkyl radical such as
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