code: def _get_columns_relevant_for_diff(columns_to_show):
      
      cols = set([col.title for col in columns_to_show if col.relevant_for_diff])
      if len(cols) == 0:
          return set(
              [col.title for col in columns_to_show if col.title == "status"])
      else:
          return cols
docs: Extract columns that are relevant for the diff table.
  
      @param columns_to_show: (list) A list of columns that should be shown
      @return: (set) Set of columns that are relevant for the diff table. If
               none is marked relevant, the column named "status" will be
               returned in the set.