prov:value
| - A is an oxygen atom or a group of the formula (a), (b) or (c) ##STR3## where R is a hydrogen atom, an amino group, an alkyl group of 1 to 6, preferably 1 to 4, carbon atoms which may be substituted by 1 or 2 substituents selected from the group consisting of amino, sulfo, hydroxy, sulfato, phosphato and carboxy, or an alkyl group of 3 to 8, preferably 3 to 5, carbon atoms which is interrupted by 1
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