Action integral
= Action integral
{title2=$I_j=\frac1{2\pi}\oint_{\gamma_j}\lambda$}
Near a regular <Lagrangian torus>, choose a one-form $\lambda$ with $d\lambda=-\omega$ and a basis of fibre cycles $\gamma_j$. The action $I_j=(2\pi)^{-1}\int_{\gamma_j}\lambda$ has <differential of a smooth map> $dI_j=(2\pi)^{-1}\sum_i t_i^{(j)}dF_i$, where $t^{(j)}$ is the corresponding joint-flow period. Nonsingularity of the period matrix makes these actions local coordinates transverse to the tori.