docs: def is_grammar_generating(grammar, remove=False):
          # type: (Grammar, bool) -> bool
          """
          Check if is grammar is generating.
          Generating grammar generates at least one sentence.
          :param grammar: Grammar to check.
          :param remove: True to remove nongenerating symbols from the grammar.
          :return: True if is grammar generating, false otherwise.
          """
          g = ContextFree.remove_nongenerating_nonterminals(grammar, remove)
          return g.start is not None