Proof. Obviously, connection $\bar{\nabla}$ does not change under the transformation $x_{j}\mapsto x_{j}+\varepsilon n_{j},n_{j}\in{\bf Z}$. The transformation $x_{j}^{\vee}\mapsto x_{j}^{\vee}+n_{j}^{\vee},n_{j}^{\vee}\in{\bf Z}$ together with the gauge transformation of $\bar{\nabla}$ by $h=exp(2\pi i/\varepsilon\sum_{j}n_{j}^{\vee}x_{j})$ also preserves $\bar{\nabla}$. This proves the Lemma. $\blacksquare$