Zachar Z.: On the equivalence of the frontier-to-root tree transducers I. In: Acta cybernetica, (7) 2. pp. 173-182. (1985)
Zachar Z.: On the equivalence of the frontier-to-root tree transducers II. In: Acta cybernetica, (7) 2. pp. 183-193. (1985)
Zachar Z.: The solvability of the equivalence problem for deterministic frontier-to-root tree transducers. In: Acta cybernetica, (4) 2. pp. 167-177. (1979)