#couple.building_block  something joined by two equal and opposite forces that act along parallel lines
  supertype:  building_block__unit  a single undivided natural entity occurring in the composition of something else; "units of nucleic acids"
  part:  moment.force
  subtype:  dipole  a pair of equal and opposite electric charges or magnetic poles separated by a small distance
     subtype:  electric_dipole__electric_doublet  a dipole with equal and opposite electric charges
     subtype:  magnetic_dipole  a dipole with opposing magnetic poles

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