code: def check_polygon(coord):
      if not isinstance(coord, list):
          return "Each polygon must be a list of linear rings"
  
      if not all(isinstance(elem, list) for elem in coord):
          return (
              "Each element of a polygon's coordinates must be a list"
          )
  
      lengths = all(len(elem) >= 4 for elem in coord)
      if lengths is False:
          return "Each linear ring must contain at least 4 positions"
  
      isring = all(elem[0] == elem[-1] for elem in coord)
      if isring is False:
          return "Each linear ring must end where it started"
  
imports: from decimal import Decimal
  from numbers import Number, Real
  from geojson.base import GeoJSON
label_desc: Use image node_id 3 for calling a global function with example usage: check_polygon(coord) and returns: str, str, str, str