@article{article6e59c424,
title   = {Rationality of the Hilbert series of Hopf-invariants of free algebras},
author = {Ferreira, Vitor de Oliveira and Murakami, Lúcia Satie Ikemoto},
year = {2014},
doi = {10.1090/S0002-9939-2013-11830-7},
journal   = {Proceedings of the American Mathematical Society}
}