Andrea Asperti, Paolo Coppola, Simone Martini. (Optimal) duplication is not elementary recursive. Inf. Comput., 193(1):21-56, 2004. [doi]
@article{AspertiCM04,
title = {(Optimal) duplication is not elementary recursive},
author = {Andrea Asperti and Paolo Coppola and Simone Martini},
year = {2004},
doi = {10.1016/j.ic.2004.05.001},
url = {http://dx.doi.org/10.1016/j.ic.2004.05.001},
researchr = {https://researchr.org/publication/AspertiCM04},
cites = {0},
citedby = {0},
journal = {Inf. Comput.},
volume = {193},
number = {1},
pages = {21-56},
}