We consider in general two-block substitutions and their fixed points. We prove that some of them have a simple structure: their fixed points are morphic sequences. Others are intrinsically more complex, such as the Kolakoski sequence. We prove this for the Thue-Morse sequence in base 3/2.

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Advances in Applied Mathematics
Centrum Wiskunde & Informatica, Amsterdam (CWI), The Netherlands

Dekking, M., & Keane, M. (2023). Two-block substitutions and morphic words. Advances in Applied Mathematics, 148, 102536:1–102536:8. doi:10.1016/j.aam.2023.102536