We shall show that the operation $+$ on the set $\NN$ of
nonnegative integers is definable from $\times$ and the
neighbourhood relation $\Neib=\set{(x,y)\in\NN^2\bigm|
|x-y|=1}$. The same result is proved for the divisibility
relation $|$ instead of $\times$. If we replace $\NN$ by the
set $\ZZ$ of all integers then $+$ is definable from $\Neib$
and $\times$ but it is not definable from $\Neib$ and
divisibility, and even from $\Neib$, divisibility and the
constant $1$. Similar results for some commutative rings are
presented.
