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Topological sums and products in ZF-set theory

机译:ZF集理论中的拓扑和和积

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摘要

In ZF, i.e., Zermelo-Fraenkel set theory without the axiom of choice, the category Top of topological spaces and continuous maps is well-behaved. In particular, Top has sums (= coproducts) and products. However, it may happen that for families (X_i)_(i∈l) and (Y_i)_(i∈l) with the property that each X_i is homeomorphic to the corresponding Y_i neither their sums ⊕_(i∈l), X_i and ⊕_(i∈l) Y_i nor their products Π_(i∈l) X_i and Π_(i∈l) Y_i are homeomorphic. It will be shown that the axiom of choice is not only sufficient but also necessary to rectify this defect.
机译:在ZF中,即没有选择公理的Zermelo-Fraenkel集合论,拓扑空间和连续图的类别Top行为良好。特别是,Top具有和(=副产品)和乘积。但是,对于族(X_i)_(i∈l)和(Y_i)_(i∈l),具有每个X_i与对应的Y_i同胚的性质,或者它们的和⊕_(i∈l)可能发生, X_i和⊕_(i∈l)Y_i或它们的乘积__(i∈l)X_i和(_(i∈l)Y_i是​​同胚的。可以看出,选择公理不仅足以纠正该缺陷,而且是必要的。

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