We have the following indirect implication of form equivalence classes:
| Implication | Reference |
|---|---|
| 60 \(\Rightarrow\) 231 |
Cardinals and the Boolean prime ideal theorem, Tsukada, N. 1977, Sci. Rep. Tokyo Kyoiku Daigaku Sect. A |
| 231 \(\Rightarrow\) 421 | clear |
Here are the links and statements of the form equivalence classes referenced above:
| Howard-Rubin Number | Statement |
|---|---|
| 60: |
\(C(\infty,WO)\): Every set of non-empty, well orderable sets has a choice function. |
| 231: | \(UT(WO,WO,WO)\): The union of a well ordered collection of well orderable sets is well orderable. |
| 421: | \(UT(\aleph_0,WO,WO)\): The union of a denumerable set of well orderable sets can be well ordered. |
Comment: