#expanse  a wide and open space or area as of surface or land or sky
  supertype:  pm#space (pm)  point or extent in space
  subtype:  #sheet  any broad thin expanse or surface: "a sheet of ice"
  subtype:  #stretch.expanse  a large and unbroken expanse or distance; "a stretch of highway"; "a stretch of clear water"
     subtype:  #slack.stretch  a stretch of water without current or movement; "suddenly they were in slack water"

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