Let G be a finitely generated torsion-free pro- p group containing an open free-by- Z pro- p subgroup. We show that the completed group algebra F G is a Sylvester domain. Moreover, the inner rank irk₅䂹 ₆ (A) of a matrix A over F G can be calculated by approximation by ranks corresponding to finite quotients of G. As a consequence, we obtain a particular case of the mod p Lück approximation for abstract finitely generated subgroups of free-by- Z pro- p groups.
Jaikin‐Zapirain et al. (Tue,) studied this question.