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KP Hart
  • Member for 14 years, 7 months
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Strong ultralimits?
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Strong ultralimits?
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Topologizing quasi orders with regards to products
A long time ago I was looking at intrinsic topologies for ordered structures and I came across a paper by Jimmie Lawson that catalogued all kinds of topologies that could be defined intrinsically on (semi)lattices. Here are links to reviews on zbMath of that paper and a related one. The latter shows that the topology of a compact topological (semi)lattice is intrinsic and unique. You'll see there's many ways to topologise a (semi)lattice; some of the ways work on partial/quasi-orders as well.
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Is this true in the ordered Mostowski model?
You can also find it as Lemma 4.5 in Jech's The Axiom of Choice.
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Is this true in the ordered Mostowski model?
In the original paper, Über die Unabhängigkeit des Wohlordnungssatzes vom Ordnungsprinzip, Fund. Math. 32 (1939), 201-252 you'll find this in statement 101 on page 243. But there is a lot of preparatory work to go through before that.
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Implicit uses of Countable or Dependent Choice
@MikhailKatz It seems that for many analysts the Axiom of Choice was unproblematic, see for example Banach's proof of the Hahn-Banach theorem in Studia Mathematica, 1 (1929), 211-216. The one-step extension is proven as Theorem 1, the full theorem is Theorem 2: On prouve ce théorème par induction transfinie en appliquant succesivement le théorème 1 aux éléments de l'ensemble $E-G$ (supposé bien ordonné).
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Implicit uses of Countable or Dependent Choice
@MikhailKatz I looked but could not find anything. Rudin certainly knew his Set Theory, but I think he was completely comfortable with the Axiom of Choice. In the proof of the Hahn-Banach theorem in Functional Analysis he does the one-step extension and then says that "The second part of the proof can be done by whatever one's favorite method of transfinite induction is; well-ordering, Zorn's lemma, or Hausdorff's maximality theorem:" He uses the last one. In the appendix he indicates where that theorem is also used in the book: Krein-Milman and the maximal-ideal theorem in rings.
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Implicit uses of Countable or Dependent Choice
Answered the question in the comments about global continuity.
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Is every connected subgroup of a Euclidean space closed?
Jones' paper is quite informative too on what is possible with discontinuous additive functions and their graphs.
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