#arc  a continuous portion of a circle
  supertype:  #curved_shape__curve  the trace of a point whose direction of motion changes
  part of:  #circle  ellipse in which the two axes are of equal length; a plane curve generated by one point moving at a constant distance from a fixed point; "he calculated the circumference of the circle"
  part of:  #sector  a plane figure bounded by two radii and the included arc of a circle

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