Alad'ev, Viktor:
Об эквивалентности $\tau_m$-грамматик и $Sb(n)$-грамматик.
(Russian) [The equivalence of $\tau_m$-grammars and $Sb(n)$-grammars].Commentationes Mathematicae Universitatis Carolinae,
vol. 15
(1974),
issue 4,
pp. 717-726
Alad'ev, Viktor:
Операции над языками, генерируемыми $\tau_n$-грамматиками.
(Russian) [Operations over languages that are generated by $\tau_n$-grammars].Commentationes Mathematicae Universitatis Carolinae,
vol. 15
(1974),
issue 2,
pp. 211-220