If G is a GGS-group defined over a p-adic tree, where p is an odd prime, we
calculate the order of the congruence quotients $G_n=G/\Stab_G(n)$ for every n.
If G is defined by the vector $e=(e_1,...,e_{p-1})\in\F_p^{p-1}$, the
determination of the order of $G_n$ is split into three cases, according as e
is non-symmetric, non-constant symmetric, or constant. The formulas that we
obtain only depend on p, n, and the rank of the circulant matrix whose first
row is e.
Let $G$ be a finite group of order $p^am$, where $p$ is a prime and $m$ is
not divisible by $p$, and let $P$ be a Sylow $p$-subgroup of $G$. If $w$ is an
outer commutator word, we prove that $P\cap w(G)$ is generated by the
intersection of $P$ with the set of $m$th powers of all values of $w$ in $G$