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Questions about the branch of algebra that deals with groups.

82 votes

Results from abstract algebra which look wrong (but are true)

The free group with infinitely many generators is a subgroup of the free group with two generators.
12 votes
Accepted

The Tall Tale of Terminating Transfinite Towers

Here is a relevant paper, Kaplan, Itay; Shelah, Saharon, The automorphism tower of a centerless group without choice, Arch. Math. Logic 48, No. 8, 799-815 (2009). ZBL1192.03026. At least for a c …
Asaf Karagila's user avatar
  • 39.8k
9 votes
3 answers
1k views

First-order axiomatization of free groups

Is there a way to axiomatize [non-abelian] free groups in first-order logic using the language of groups (which contains the binary operation symbol $\cdot$, and the constant symbol $e$)? Is there on …
Asaf Karagila's user avatar
  • 39.8k
7 votes
Accepted

Number of torsion-free abelian groups

You can construct antichains of size $\frak c$ without using choice, you can even have them to be antichains in a stronger sense of the word: i.e. every two have a finite intersection. The one thing …
Asaf Karagila's user avatar
  • 39.8k