#building_block__unit  a single undivided natural entity occurring in the composition of something else; "units of nucleic acids"
  supertype:  pm#physical_entity_part_or_substance (pm)
  subtype:  #chemical_chain  #couple.building_block  #unit_cell  #chemical_group  #molecule
  part:  #physical_part__part__piece  a portion of a natural object; "they analyzed the river into three parts"; "he needed a piece of granite"

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