The Word Problem for Free Fields. - P. M. Cohn (J. Symb. Log., 1973)

The Word Problem for Free Fields: A Correction and an Addendum. - P. M. Cohn (J. Symb. Log., 1975)

On the Construction of the Free Field. - P. M. Cohn; Christophe Reutenauer (Int. J. Algebra Comput., 1999)