#trigon__triangle__trilateral  a three-sided polygon
  supertype:  #polygon__polygonal_shape__polygonalshape  a closed plane figure bounded by straight sides
  subtype:  #acute_triangle__acutetriangle__acute-angled_triangle  a triangle whose interior angles are all acute
  subtype:  #equilateral_triangle__equilateraltriangle__equiangular_triangle__equiangulartriangle  a three-sided regular polygon
  subtype:  #isosceles_triangle__isoscelestriangle  a triangle with two equal sides
  subtype:  #oblique_triangle__obliquetriangle  a triangle that contains no right angle
  subtype:  #obtuse_triangle__obtuse-angled_triangle  a triangle that contains an obtuse interior angle
  subtype:  #right_triangle__righttriangle__right-angled_triangle  a triangle with one right angle
  subtype:  #scalene_triangle__scalenetriangle  a triangle with no two sides of equal length
  subtype:  #wedge_shape__wedgeshape__wedge__cuneus  any shape that is triangular in cross section

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