prov:value
| - represents 0 or 1, ##STR3## wherein R.sup.2 represents a hydrogen atom or an alkyl, cycloalkyl, alkenyl, aralkyl, aryl, alkoxy or --CONHR group (R is a hydrogen atom or an alkyl, aryl, alkylthio, arylthio, alkylsulfonyl or arylsulfonyl group) or a
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