Timeline for Is "square" functor monomorphic on objects?
Current License: CC BY-SA 3.0
5 events
| when toggle format | what | by | license | comment | |
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| Oct 16, 2017 at 22:23 | comment | added | Jeremy Rickard | Just a historical comment: Whether there are non-isomorphic abelian groups with $A\times A\cong B\times B$ was Kaplansky’s second “test problem” from 1954, and the first example was published by Jonsson in 1957, long before anybody looked for examples of abelian groups with $A\times\mathbb{Z}\not\cong A\cong A\times\mathbb{Z}\times\mathbb{Z}$. | |
| Oct 16, 2017 at 20:56 | comment | added | Almeo Maus | thank you so much!! This counter-example with groups is perfect. | |
| Oct 16, 2017 at 20:55 | vote | accept | Almeo Maus | ||
| Oct 16, 2017 at 20:49 | comment | added | Will Sawin | see also the Boolean algebra counterexample mathoverflow.net/a/227525/18060 | |
| Oct 16, 2017 at 20:45 | history | answered | Will Sawin | CC BY-SA 3.0 |