Problem #5
Does the Partition Principle imply the Axiom of Choice?
The Partition Principle () states: if there is a surjection from a set onto a set (equivalently, admits a partition into at most nonempty blocks), then there is an injection from into . In (without choice), follows from the Axiom of Choice (), but whether
is one of the oldest open problems concerning choice principles, going back to the early 1900s.
Reference for the problem statement
Herman Rubin and Jean E. Rubin, Equivalents of the Axiom of Choice II, North-Holland, 1985
Definitions
- : Zermelo–Fraenkel set theory without the Axiom of Choice.
- Partition Principle (): for sets , if there is a surjection , then there is an injection .
- Axiom of Choice (): every family of nonempty sets has a choice function.
Known Partial Results
- is known to imply several weaker choice-like consequences.
- has been shown equivalent to under various additional hypotheses, but no such additional hypothesis is known to be eliminable in general.
- The problem has resisted both a proof of the implication and the construction of a permutation/symmetric or forcing model separating from .
Notes
This problem is notable for its longevity — it has remained open for over a century despite being one of the most natural questions one can ask about weak forms of choice, and despite extensive work relating to essentially every other known choice principle.
Additional References
- Rubin, H. and Rubin, J. E. "Equivalents of the Axiom of Choice II." North-Holland, 1985 (catalogs known implications among choice principles, including this one).
- Halbeisen, L. "Combinatorial Set Theory: With a Gentle Introduction to Forcing." Springer, 2012 (survey of choice principles, including ).
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