  Let $S$ be a semigroup and $T$ be a subsemigroup of finite index in $S$ (that
is, the set $S\setminus T$ is finite). The subsemigroup $T$ is also called a
large subsemigroup of $S$. It is well known that if $T$ has a finite complete
rewriting system then so does $S$. In this paper, we will prove the converse,
that is, if $S$ has a finite complete rewriting system then so does $T$. Our
proof is purely combinatorial and also constructive.
