prov:value
| - B) compounds of formula II, III or IV ##STR2## wherein each of R11, R12 and R13, independently of the others, is a hydrogen atom or a C3 -C10 alkenyl group, at least one of the radicals R11 to R13 being an alkenyl group, ##STR3## wherein Q is a direct bond, methylene, 2,2-propylidene, --CO--, --O--, --S--, --SO-- or --SO2 -- and each of R14, R15, R16 and R17, independently of the others, is a hydr
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