Skip to main content
Notice removed Reward existing answer by David E Speyer
Bounty Ended with Harry West's answer chosen by David E Speyer
Notice added Reward existing answer by David E Speyer
Bounty Started worth 250 reputation by David E Speyer
edited tags
Link
YCor
  • 63.9k
  • 5
  • 187
  • 286
replaced http://mathoverflow.net/ with https://mathoverflow.net/
Source Link

In ZFC, some homomorphisms from profinite groups to finite groups are discontinuous. For instance, see the examples in this questionthis question. However, all three constructions given use consequences of the axiom of choice: ultrafilters in the first answer, and "every vector space has a basis", in Milne's notes as referenced in the second answer, and used to compute the number of finite-index subgroups in the third answer.

Is it possible to prove the existence of a discontinuous homomorphism from a profinite group to a finite group without the axiom of choice? Instead is it consistent with ZF that there is none?

In ZFC, some homomorphisms from profinite groups to finite groups are discontinuous. For instance, see the examples in this question. However, all three constructions given use consequences of the axiom of choice: ultrafilters in the first answer, and "every vector space has a basis", in Milne's notes as referenced in the second answer, and used to compute the number of finite-index subgroups in the third answer.

Is it possible to prove the existence of a discontinuous homomorphism from a profinite group to a finite group without the axiom of choice? Instead is it consistent with ZF that there is none?

In ZFC, some homomorphisms from profinite groups to finite groups are discontinuous. For instance, see the examples in this question. However, all three constructions given use consequences of the axiom of choice: ultrafilters in the first answer, and "every vector space has a basis", in Milne's notes as referenced in the second answer, and used to compute the number of finite-index subgroups in the third answer.

Is it possible to prove the existence of a discontinuous homomorphism from a profinite group to a finite group without the axiom of choice? Instead is it consistent with ZF that there is none?

Added AC tag.
Link
Asaf Karagila
  • 39.7k
  • 8
  • 134
  • 282
Source Link
Will Sawin
  • 148.4k
  • 9
  • 324
  • 563
Loading