code: def find_subscript_name(subscript_dict, element):
      
      if element in subscript_dict.keys():
          return element
  
      for name, elements in subscript_dict.items():
          if element in elements:
              return name
docs: Given a subscript dictionary, and a member of a subscript family,
      return the first key of which the member is within the value list.
      If element is already a subscript name, return that
  
      Parameters
      ----------
      subscript_dict: dictionary
          Follows the {'subscript name':['list','of','subscript','elements']} format
  
      element: string
  
      Returns
      -------
  
      Examples:
      >>> find_subscript_name({'Dim1': ['A', 'B'],
      ...                      'Dim2': ['C', 'D', 'E'],
      ...                      'Dim3': ['F', 'G', 'H', 'I']},
      ...                      'D')
      'Dim2'