prov:value
| - with the proviso that (Y1)n???(Y2)m does not include O???O, or S???O groups;each of R1, R2 and R3, independently of the others, is hydrogen, lower alkyl, especially methyl, ethyl, n-propyl, isopropyl or tert-butyl, lower alkenyl, especially isopropenyl, hydroxy-lower alkyl, especially hydroxy-propyl, lower alkoxy, especially methoxy, halo, especially chloro or bromo, halo-lower alkyl, especially t
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