Consider the coordinates $(b_{1},b_{2},b_{3})$ on $B=D^{2}\times D^{1}$ and the period lattice as in Proposition 4.8. With respect to these coordinates $\Delta=\{b_{1}=b_{2}=0\}$. Define open subsets of $B_{0}=B-\Delta$:

	$\displaystyle V_{1}$	$\displaystyle=$	$\displaystyle B-\{(b_{1},0,b_{3})\ |\ b_{1}>0\},$
	$\displaystyle V_{2}$	$\displaystyle=$	$\displaystyle B-\{(b_{1},0,b_{3})\ |\ b_{1}<0\}.$

On $V_{j}$ the action coordinates have the form

$$A_{j}(b_{1},b_{2},b_{3})=(\psi_{j}(b_{1},b_{2})+H(b_{1},b_{2},b_{3}),2\pi b_{2},b_{3}),$$

where $\psi_{j}$ is a choice of primitive of $\lambda_{0}$. Then $\mathscr{A}=\{U_{j},A_{j}\}$ gives the integral affine structure on $B_{0}$. As in the focus-focus case, for either $j=1,2$, the map $A_{j}$ extends to a homeomorphism, $A:B\rightarrow A(B)\subseteq\mathbb{R}^{2}\times\mathbb{R}$ such that $A(0)=0$. It is easy to show that, if $\tau(t)=H(0,0,t)$, then $A$ is an isomorphism between $(B,\Delta,\mathscr{A})$ and a neighborhood of $\Delta_{\tau}$ in the affine manifold with singularities of Example 3.9. ∎