code: def relative_field(field, parent):
      
      if parent==".":
          return field
  
      field_path = split_field(field)
      parent_path = split_field(parent)
      common = 0
      for f, p in _builtin_zip(field_path, parent_path):
          if f != p:
              break
          common += 1
  
      if len(parent_path) == common:
          return join_field(field_path[common:])
      else:
          dots = "." * (len(parent_path) - common)
          return dots + "." + join_field(field_path[common:])
docs: RETURN field PATH WITH RESPECT TO parent