Explicit Koszul-dualizing bimodules in bordered Heegaard Floer homology

We give a combinatorial proof of the quasi-invertibility of $\widehat{CFDD}(\mathbb{I}_\mathcal{Z})$ in bordered Heegaard Floer homology, which implies a Koszul self-duality on the dg-algebra $\mathcal{A}(\mathcal{Z})$, for each pointed matched circle $\mathcal{Z}$. This is done by giving an explicit description of a rank 1 model for $\widehat{CFAA}(\mathbb{I}_\mathcal{Z})$, the quasi-inverse of $\widehat{CFDD}(\mathbb{I}_\mathcal{Z})$. This description is obtained by applying homological perturbation theory to a larger, previously known model of $\widehat{CFAA}(\mathbb{I}_\mathcal{Z})$.