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Asaf Karagila
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The counterpart you may intend to use is that every cardinal is comparable with $\kappa$. This means that every infinite set which is not smaller than $\kappa$ has a subset of cardinality $\kappa$.

This is the restriction of the well-ordering principle to $\kappa$, whereas $\sf AC_\kappa$ is the restriction of the axiom of choice to families of size at most $\kappa$.

It should be noted that $\sf WO_\kappa$ does not imply $\sf AC_\kappa$, and the other way around is true only if $\sf WO_{<\kappa}$ holds and $\sf AC_{\operatorname{cf}(\kappa)}$ holds for limit cardinals.

For more on that, see Jech The Axiom of Choice, Chapter 8.

Your idea, bywhile interesting has a problem that we can't really control the idea is not going to workcardinality of the sets in $V_\kappa$. It is consistentWe would like something that we can add an infinite setsomewhat control, which have no countably infinite subsetis comparability of cardinals. In a sense the well-ordering principle is just a prelude to the trichotomy theorem (every two cardinals are comparable), and its rankso this is arbitrarily highwhat we want to limit.

In the same breath, I should mention that my philosophy is that $\sf DC_\kappa$ is the true restriction of $\sf AC$ to $\kappa$, being stronger than the two principles above, and corresponding to Zorn's lemma (or maybe Hausdorff's maximality principle).

The counterpart you may intend to use is that every cardinal is comparable with $\kappa$. This means that every infinite set which is not smaller than $\kappa$ has a subset of cardinality $\kappa$.

This is the restriction of the well-ordering principle to $\kappa$, whereas $\sf AC_\kappa$ is the restriction of the axiom of choice to families of size at most $\kappa$.

It should be noted that $\sf WO_\kappa$ does not imply $\sf AC_\kappa$, and the other way around is true only if $\sf WO_{<\kappa}$ holds and $\sf AC_{\operatorname{cf}(\kappa)}$ holds for limit cardinals.

For more on that, see Jech The Axiom of Choice, Chapter 8.

Your idea, by the idea is not going to work. It is consistent that we can add an infinite set which have no countably infinite subset, and its rank is arbitrarily high.

The counterpart you may intend to use is that every cardinal is comparable with $\kappa$. This means that every infinite set which is not smaller than $\kappa$ has a subset of cardinality $\kappa$.

This is the restriction of the well-ordering principle to $\kappa$, whereas $\sf AC_\kappa$ is the restriction of the axiom of choice to families of size at most $\kappa$.

It should be noted that $\sf WO_\kappa$ does not imply $\sf AC_\kappa$, and the other way around is true only if $\sf WO_{<\kappa}$ holds and $\sf AC_{\operatorname{cf}(\kappa)}$ holds for limit cardinals.

For more on that, see Jech The Axiom of Choice, Chapter 8.

Your idea, while interesting has a problem that we can't really control the cardinality of the sets in $V_\kappa$. We would like something that we can somewhat control, which is comparability of cardinals. In a sense the well-ordering principle is just a prelude to the trichotomy theorem (every two cardinals are comparable), so this is what we want to limit.

In the same breath, I should mention that my philosophy is that $\sf DC_\kappa$ is the true restriction of $\sf AC$ to $\kappa$, being stronger than the two principles above, and corresponding to Zorn's lemma (or maybe Hausdorff's maximality principle).

Source Link
Asaf Karagila
  • 39.8k
  • 8
  • 135
  • 283

The counterpart you may intend to use is that every cardinal is comparable with $\kappa$. This means that every infinite set which is not smaller than $\kappa$ has a subset of cardinality $\kappa$.

This is the restriction of the well-ordering principle to $\kappa$, whereas $\sf AC_\kappa$ is the restriction of the axiom of choice to families of size at most $\kappa$.

It should be noted that $\sf WO_\kappa$ does not imply $\sf AC_\kappa$, and the other way around is true only if $\sf WO_{<\kappa}$ holds and $\sf AC_{\operatorname{cf}(\kappa)}$ holds for limit cardinals.

For more on that, see Jech The Axiom of Choice, Chapter 8.

Your idea, by the idea is not going to work. It is consistent that we can add an infinite set which have no countably infinite subset, and its rank is arbitrarily high.