[1] Backus J. W., Bauer F. L., Green J., Katz C, McCarthy J., Naur P. (editor), Perlis A. J., Rutishauser H., Samelson K., Vauguois E., Wegstein J. H., van Wijugaarden A., Woodger M.: Reports on the Algorithmic Language ALGOL 60. Numer. Math. 2 (1960), 106-136.

[2] Čulik K.: On eguivalent and similar grammars of ALGOL-like languages. Comment. math. Univ. carolinae 5 (1964), 93-95. MR 0167351

[3] Chomsky N.: On certain Formal Properties of Grammars. Inform. and Control 2 (1959), 137-167. MR 0105365 | Zbl 0161.00804

[4] Fabian V.: Structural unambiguity of formal languages. Czechosl. Math. J. 14 (88) (1964), 394-430. MR 0171639 | Zbl 0278.68062

[5] Gruska J.: On structural unambiguity of formal languages. Czechosl. Math. J. 15 (89) (1965), 283-294. MR 0220549 | Zbl 0133.25503

[6] Gruska J.: Structural unambiguity of ALGOL MOD. Comment. math. Univ. carolinae 6 (1965), 281-328. MR 0207487 | Zbl 0139.00802