Lemma 4.3 . [05DW]

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Lemma 4.3.

The operator $D_{\sigma}\mathfrak{F}_{k}(0,0)$ is invertible for $k\gg 1$ , and

\|D_{\sigma}\mathfrak{F}_{k}(0,0)^{-1}\|\leq\overline{C},

for a constant $\overline{C}>0$ independent of $k$ .