We are grateful to Ikkei Hotta for his detailed comments on complex analysis. The results of T.T. (Sects. 6, 7 and Appendix) is an output of a research project implemented as part of the Basic Research Program at the National Research University Higher School of Economics. T.T. also thanks Rikkyo University for hospitality, where a part of this work was done. The work of A.Z. (Sects. 2–5) was performed at the Steklov Mathematical Institute of Russian Academy of Sciences, Moscow, and was supported by the Russian Science Foundation under Grant 19-11-00062.
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