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An important and fundamental axiom in set theory sometimes called Zermelo's axiom of choice. It was formulated by Zermelo in 1904 and states that, given any set of mutually disjoint nonempty sets, there exists at least one set that contains exactly one element in common with each of the nonempty sets. The axiom of choice is related to the first of Hilbert's problems.

10 votes
0 answers
270 views

Strength of claims about extensions of partial preorders and orders to linear ones

Consider these two axioms: Every partial order extends to a linear order. Every partial preorder (reflexive and transitive relation) extends to a linear preorder while preserving strict orderings: i. …
Alexander Pruss's user avatar
20 votes
0 answers
449 views

Hahn-Banach and the "Axiom of Probabilistic Choice"

Stipulate that the Axiom of Probabilistic Choice (APC) says that for every collection $\{ A_i : i \in I \}$ of non-empty sets, there is a function on $I$ that assigns to $i$ a finitely-additive probab …
Alexander Pruss's user avatar
21 votes
Accepted

Probabilities in a riddle involving axiom of choice

The probabilistic reasoning depends on a conglomerability assumption, namely that given a fixed sequence $\vec u$, the probability of guessing correctly is $(n-1)/n$, then for a randomly selected sequ …
Alexander Pruss's user avatar
10 votes

Unique existence and the axiom of choice

In A definable nonstandard model of the reals, Kanovei and Shelah surprisingly managed to prove the existence of a ZFC-definable (i.e., specifiable via an explicit ZFC construction) nonstandard model …
Alexander Pruss's user avatar
3 votes

Strength of some claims about finitely additive measures on infinite sets?

A quick note that (2) doesn't follow from ZF (assuming ZF is consistent) or even ZF+DC. (2)+Countable Choice for Finite Sets (CC(fin)) implies that every uncountable set has a non-principal (finite …
Alexander Pruss's user avatar
6 votes
4 answers
609 views

Strength of some claims about finitely additive measures on infinite sets?

Assume ZF. Consider the claim: (1) For any infinite set $\Omega$, there is a finitely additive probability measure $\mu:2^\Omega\to[0,1]$ with $\mu(A) = 0$ whenever $|A|<|\Omega|$. Then (1) is impl …
Alexander Pruss's user avatar
10 votes
0 answers
755 views

Full conditional probabilities and versions of AC?

A probability is a finitely additive measure on a boolean algebra with total measure $1$. A function $P:\scr B \times (\scr B - \{ 0 \})$ is a full conditional probability on $\scr B$ (for a boolean …