#line_of_force__field_line__fieldline  an imaginary line in a field of force; direction of the line at any point is the direction of the force at that point
  supertype:  line.location  a spatial location defined by a real or imaginary unidimensional extent
  subtype:  electrical_line_of_force  a line of force in an electrical field
  subtype:  magnetic_line_of_force  a line of force in a magnetic field

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