| http://www.w3.org/ns/prov#value | - ##STR00007## in which R.sub.20 represents a hydrogen atom or a CH.sub.3O, CH.sub.3CH.sub.2O or phenyl radical R.sub.21 denotes hydrogen or a lower alkyl radical, such as methyl or ethyl, R.sub.22 denotes hydrogen or a lower alkyl radical, such
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