Bergeron, Nantel; Zabrocki, Mike (2009), "The Hopf algebras of symmetric functions and quasi-symmetric functions in non-commutative variables are free and co-free", Journal of Algebra and Its Applications, 8 (4): 581–600, arXiv:math/0509265, doi:10.1142/S0219498809003485, S2CID18601994
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Bergeron, Nantel; Zabrocki, Mike (2009), "The Hopf algebras of symmetric functions and quasi-symmetric functions in non-commutative variables are free and co-free", Journal of Algebra and Its Applications, 8 (4): 581–600, arXiv:math/0509265, doi:10.1142/S0219498809003485, S2CID18601994
Bergeron, Nantel; Zabrocki, Mike (2009), "The Hopf algebras of symmetric functions and quasi-symmetric functions in non-commutative variables are free and co-free", Journal of Algebra and Its Applications, 8 (4): 581–600, arXiv:math/0509265, doi:10.1142/S0219498809003485, S2CID18601994