| http://www.w3.org/ns/prov#value | - Also suitable as ???B??? groups are urea groups, including those of the general formulae wherein, provided that at least one of R1, R2, and R3 is a hydrogen atom, R1, R2 and R3 each can be a hydrogen atom, an alkyl group (including linear, branched, cyclic, saturated, unsaturated, and substituted alkyl groups, and wherein hetero atoms, such as oxygen, sulfur, nitrogen, silicon, or the like, can be
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