#coordinate_axis  one of the fixed reference lines of a coordinate system
  supertype:  #axis  a straight line through a body or figure that satisfies certain conditions
  part of:  #coordinate_system
  subtype:  #x-axis  the horizontal axis in a plane coordinate system
  subtype:  #y-axis  the vertical axis in a plane coordinate system
  subtype:  #z-axis  the third axis in a 3-dimensional coordinate system

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