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12h
revised Weights on cyclic orderings
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12h
revised What kind of category is a cyclically ordered set?
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1d
revised Fibered products of cyclic groups
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1d
revised Cyclically symmetric functions
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1d
revised Finitely generated subgroups are cyclic, and a generalization
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2d
wiki created computational-topology description
2d
wiki created computational-topology excerpt
Feb
5
answered Can tests for the convergence and divergence of series be used to create undecidable sentences?
Jan
30
comment Reference request: Models of isomorphic languages result into isomorphic categories
Hájek's article is here: digizeitschriften.de/dms/img/?PID=GDZPPN002043920 You asked for a reference for the fact that "isomorphic languages should result into isomorphic categories [of models]"; Hájek does quite a lot more since he considers translations that aren't just symbol substitutions. I doubt the trivial case you're interested in has been published on its own.
Jan
30
comment Reference request: Models of isomorphic languages result into isomorphic categories
OK. I think you're homing in on the idea of 'syntactic model' of Petr Hájek [Logische Kategorien, Arch. Math. Logik Grundlagenforsch. 13 1970 168–193] though Hájek pursues the idea in far too much generality for your purposes.
Jan
30
comment Reference request: Models of isomorphic languages result into isomorphic categories
See also Adámek & Rosicky Locally Presentable and Accessible Categories.
Jan
30
comment Reference request: Models of isomorphic languages result into isomorphic categories
Never mind, I figured out what was confusing me in the wording. Are you looking for something different than a special case of 'interpretation' - wikiwand.com/en/Interpretation_%28model_theory%29 - or are you wondering about the leap to infinitary logic?
Jan
30
comment Reference request: Models of isomorphic languages result into isomorphic categories
I'm a little confused by the end of the question. Are you looking for a definition of 'model' or a definition of 'interpretation'?
Jan
21
answered a variant of the Kleene tree
Jan
20
awarded  Good Answer
Jan
17
awarded  Nice Answer
Jan
15
revised Compactness in Bishop's constructive mathematics
citation
Jan
14
comment Is there an uncountable Borel almost disjoint family?
I think it's a typo: the proposed "weak" definition of almost disjointness leads to families that are not at all disjoint in any typical sense. For example, $\{(-\infty,x)\cap\mathbb{Q}: x \in \mathbb{R}\}$.
Jan
13
comment Are the closed and unbounded subsets of $\mathbb{R}$ known up to homeomorphism?
@ChristianRemling: True, but "non-compact" would be more appropriate, I think.
Jan
12
comment Are the closed and unbounded subsets of $\mathbb{R}$ known up to homeomorphism?
"unbounded" is not a topological invariant (e.g. $(0,1)$ is homeomorphic with $(0,\infty)$).