Изменения

*[http://ru.wikipedia.org/wiki/Лемма_Огдена Wikipedia {{---}} Лемма Огдена]*''Hopcroft, Motwani and Ullman '' {{---}} Automata Theory, Languages, and Computation {{---}} Addison-Wesley, 1979. ISBN 81-7808-347-7.*''Ogden, W. '' (1968). "A helpful result for proving inherent ambiguity". Mathematical Systems Theory. 2 (3): 191–194.*[http://archive.numdam.org/ARCHIVE/ITA/ITA_1978__12_3/ITA_1978__12_3_201_0/ITA_1978__12_3_201_0.pdf On languages satisfying Ogden's lemma]*[http://ccf.ee.ntu.edu.tw/~yen/courses/toc14/chapter-2a.pdf Ogden's lemma]