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November 21, 2024, at 11:43 AM | MathWiki / MathWiki / IsomorphismProblem |
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IsomorphismProblem(1) Let $(N,\Phi)$ be a Ferrero pair with finite $N$. Let $f:N\to N$ be a group automorphism. Then $f$ is an automorphism of $(N,\mathcal B_\Phi)$ if and only if $f$ normalizes $\Phi$ in $\mathrm{Aut}(N,+)$. (Some condition on order of $N$ is required.) (2) Let $(N,\Phi)$ be a Ferrero pair with finite $N$. Let $S_1$ and $S_2$ be two complete sets of orbit representatives of $\Phi$ in $N^*=N\setminus\{0\}$. Let $*_1$ and $*_2$ be the multiplications on $N$ induced by $S_1$ and $S_2$ respectively. Then an automorphism of $(N,+)$ is an isomorphism of $(N,+,*_1)$ and $(N,+,*_2)$ if and only if $f$ normalizes $\Phi$. Questions: Is there any connection between these two theorems? Question: Classify the planar nearrings defined on the Euclidean space $\mathbb R^2$. |
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