  We observe that the determinant of the representation provides a little
restriction for the structure of the graded quotients $\mathcal{G}_k^Q{F}$
introduced in both [Algebr. Geom. Topol. 1 (2001) 39-55] and [J. Knot Theory
Ramifications 13 (2004) 297-306] that any one of them does not contain the
trivial 1-dimensional summand.
