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Register a new userA remark on locally direct product subsets in a topological Cartesian space
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Authors
Hiroki Yagisita
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Let $X$ and $Y$ be topological spaces. Let $C$ be a path-connected closed set of $Xtimes Y$. Suppose that $C$ is locally direct product, that is, for any $(a,b)in Xtimes Y$, there exist an open set $U$ of $X$, an open set $V$ of $Y$, a subset $I$ of $U$ and a subset $J$ of $V$ such that $(a,b) in Utimes V$ and $$Ccap (Utimes V)=Itimes J$$ hold. Then, in this memo, we show that $C$ is globally so, that is, there exist a subset $A$ of $X$ and a subset $B$ of $Y$ such that $$C=Atimes B$$ holds. The proof is elementary. Here, we note that one might be able to think of a (perhaps, open) similar problem for a fiber product of locally trivial fiber spaces, not just for a direct product of topological spaces. In Appendix, we mentioned a simple example of a $C([0,1];mathbb R)$-manifold that cannot be embedded in the direct product $(C([0,1];mathbb R))^n$ as a $C([0,1];mathbb R)$-submanifold. In addition, we introduce the concept of topological 2-space, which is locally the direct product of topological spaces and an analog of homotopy category for topological 2-space. Finally, we raise a question on the existence of an $mathbb R^n$-Morse function and the existence of an $mathbb R^n$-immersion in a finite-dimensional $mathbb R^n$-Euclidean space. Here, we note that the problem of defining the concept of an $mathbb R^n$-handle body may also be considered.
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