#indentation.concave_shape  a concave shape in a surface or edge or coastline etc.
  supertype:  concave_shape__concaveshape__concavity  a shape that curves inward
  subtype:  notch.indentation  a V-shaped or U-shaped indentation carved or scratched into a surface; "there were four notches in the handle of his revolver"
     subtype:  serration  a single notch in a row of notches; "one of the serrations was broken off"
        subtype:  sawtooth  a serration on a saw blade
     subtype:  thumb_index__thumbindex  one of a series of rounded notches in the fore edge of a book to indicate sections
  subtype:  notch  a V-shaped indentation; "mandibular notch"
     subtype:  incisure__incisura  (anatomy) a notch or small hollow
        subtype:  mandibular_notch  small indentation in the middle of the lower jawbone
  subtype:  cleft  a split or indentation in something (as the palate or chin)

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