prov:value
| - --S-- or a group --NH-- or --N(CH3)--), --NR5 COR6 (where R5 represents a hydrogen atom or a C1-4 alkyl group, and R6 represents a hydrogen atom or a C1-4 alkyl, C1-4 alkoxy, phenyl or --NR3 R4 group), --NR5 SO2 R7 (where R7 represents a C1-4 alkyl, phenyl or --NR3 R4 group), --COR8 (where R.sup. 8 represents hydroxy, C1-4 alkoxy or --NR3 R4), --SR9 (where R9 is a hydrogen atom, or a C1-4 alkyl or
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