@article{RSMUP_1987__77__207_0,
     author = {Wiegold, James},
     title = {A non-commutative free algebra of rank $0$},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     pages = {207--211},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {77},
     year = {1987},
     mrnumber = {904622},
     zbl = {0625.08006},
     language = {en},
     url = {http://www.numdam.org/item/RSMUP_1987__77__207_0/}
}