Theory of Computing Systems ( IF 0.6 ) Pub Date : 2020-11-13 , DOI: 10.1007/s00224-020-10017-6 Matea Čelar , Zvonko Iljazović
We examine conditions under which a semicomputable set in a computable topological space is computable. In particular, we examine topological pairs (A, B) with the following property: if X is a computable topological space and \(f:A\rightarrow X\) is an embedding such that f(A) and f(B) are semicomputable sets in X, then f(A) is a computable set in X. Such pairs (A, B) are said to have computable type. It is known that \((\mathcal {K},\{a,b\})\) has computable type if \(\mathcal {K}\) is a Hausdorff continuum chainable from a to b. It is also known that (In, ∂In) has computable type, where In is the n-dimensional unit cube and ∂In is its boundary in \(\mathbb {R}^{n} \). We generalize these results by proving the following: if \(\mathcal {K}_{i} \) is a nontrivial Hausdorff continuum chainable from ai to bi for \(i\in \{1,{\dots } ,n\}\), then \(({\prod }_{i=1}^{n} \mathcal {K}_{i} ,B)\) has computable type, where B is the set of all \((x_{1} ,{\dots } ,x_{n})\in {\prod }_{i=1}^{n} \mathcal {K}_{i}\) such that xi ∈{ai, bi} for some \(i\in \{1,{\dots } ,n\}\).
中文翻译:
可链接连续体乘积的可计算性
我们研究了可计算拓扑空间中的半计算集可计算的条件。特别是,我们检查具有以下属性的拓扑对(A,B):如果X是可计算的拓扑空间,并且\(f:A \ rightarrow X \)是一个嵌入,使得f(A)和f(B)为X中的半可计算集合,则f(A)是X中的可计算集合。此类对(A,B)具有可计算类型。已知\((\ mathcal {K},\ {a,b \})\)如果\(\ mathcal {K} \)是可从a链接到b的Hausdorff连续体,则具有可计算的类型。还已知的是(我Ñ,∂我Ñ)具有可计算的类型,其中我Ñ是Ñ维单位立方体和∂我Ñ是其边界在\(\ mathbb {R} ^ {N} \) 。我们通过证明以下概括这些结果:如果\(\ mathcal {K} _ {I} \)是一个非平凡的Hausdorff连续环连接从一个我到b我为\(I \在\ {1,{\点}, n \} \),则\(({{prod} _ {i = 1} ^ {n} \ mathcal {K} _ {i},B)\)具有可计算类型,其中B是所有\((x_ {1 },{\点},X_ {N})\在{\ PROD} _ {i = 1} ^ {N} \ mathcal {K} _ {I} \),使得X我∈{一个我,b我}表示\(i \ in \ {1,{\ dots},n \} \)。