Andrzej Ehrenfeucht, Grzegorz Rozenberg. Grammatical codes of trees. Discrete Applied Mathematics, 32(2):103-129, 1991. [doi]
@article{EhrenfeuchtR91,
title = {Grammatical codes of trees},
author = {Andrzej Ehrenfeucht and Grzegorz Rozenberg},
year = {1991},
doi = {10.1016/0166-218X(91)90095-E},
url = {http://dx.doi.org/10.1016/0166-218X(91)90095-E},
researchr = {https://researchr.org/publication/EhrenfeuchtR91},
cites = {0},
citedby = {0},
journal = {Discrete Applied Mathematics},
volume = {32},
number = {2},
pages = {103-129},
}