International audience Consider a pair of $\textit{interlacing regular convex polygons}$, each with $2(n + 2)$ vertices, which we will be referring to as $\textit{red}$ and $\textit{black}$ ones. One can place these vertices on the unit circle $|z | = 1$ in the complex plane; the vertices of the red polygon at $\epsilon^{2k}, k = 0, \ldots , 2n − 1$, of the black polygon at $\epsilon^{2k+1}, k = 0, \ldots , 2n − 1$; here $\epsilon = \exp(i \pi /(2n + 2))$. We assign to the vertices of each

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... on alternating (within each polygon) signs. Note that all the pairwise intersections of red and black sides are oriented consistently. We declare the corresponding orientation positive.