Solution
= Solution
Choose a fundamental parallelogram with no pole on its boundary. Opposite sides are translates traversed in opposite directions, so periodicity gives
$$
\oint_{\partial P}f(z)\,dz=0.
$$
The residue theorem then gives
$$
\sum_j\operatorname{Res}(f;z_j)=0.
$$
A lone simple pole has a nonzero residue by definition of its order, so an elliptic <function> cannot have exactly one simple pole in a fundamental cell.