Abstract
The fundamental theorem of affine geometry says that if a self-bijection f of an affine space of dimenion n over a possibly skew field takes left affine subspaces to left affine subspaces of the same dimension, then f of the expected type, namely f is a composition of an affine map and an automorphism of the field. We prove a two-sided analogue of this: namely, we consider self-bijections as above which take affine subspaces to affine subspaces but which are allowed to take left subspaces to right ones and vice versa. We show that under some conditions these maps again are of the expected type.
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Acknowledgements
I am grateful to the referees for their careful reading of the paper, their comments and finding a mistake in the statement of the main theorem in the first version of the paper.
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Gorinov, A. Two-Sided Fundamental Theorem of Affine Geometry. Arnold Math J. 8, 469–480 (2022). https://doi.org/10.1007/s40598-022-00201-6
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DOI: https://doi.org/10.1007/s40598-022-00201-6