  We investigate closure results for C-approximable groups, for certain classes
C of groups with invariant length functions. In particular we prove, each time
for certain (but not necessarily the same) classes C that (i) the direct
product of two C-approximable groups is C-approximable; (ii) the restricted
standard wreath product G wr H is C-approximable when G is C-approximable and H
is residually finite; and (iii) a group G$ with normal subgroup N is
C-approximable when N is C-approximable and G/N is amenable. Our direct product
result is valid for LEF, weakly sofic and hyperlinear groups, as well as for
all groups that are approximable by finite groups equipped with
commutator-contractive invariant length functions (considered in \cite{Thom}).
Our wreath product result is valid for weakly sofic groups, and we prove it
separately for sofic groups. We note that this last result has recently been
generalised by Hayes and Sale, who prove that the restricted standard wreath
product of any two sofic groups is sofic. Our result on extensions by amenable
groups is valid for weakly sofic groups, and was proved by Elek and Szabo for
sofic groups N.
