Timeline for Example of an unnatural isomorphism
Current License: CC BY-SA 3.0
6 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 26, 2019 at 16:12 | comment | added | Joshua Grochow | @TimothyChow: If we only consider these on the category of groups & isomorphisms, then we can take $F_2$ to be contravariant as well. Yet even in that situation, I think the answers on the question linked to by Eric rule out a natural isomorphism of these functors. | |
| Jun 26, 2019 at 2:14 | comment | added | Timothy Chow | As explained in the closely related question that you linked to, it probably makes most sense to think of one functor as covariant and the other contravariant. If you buy this, then the OP has ruled out this type of example by fiat. | |
| Apr 13, 2017 at 12:58 | history | edited | CommunityBot |
replaced http://mathoverflow.net/ with https://mathoverflow.net/
|
|
| Aug 15, 2013 at 2:11 | history | made wiki | Post Made Community Wiki by Ben Webster♦ | ||
| Aug 14, 2013 at 19:29 | comment | added | Eric Wofsey | There's no ambiguity on how to define $F_2$ for isomorphisms of groups, and already in that case $F_1$ and $F_2$ cannot be naturally isomorphic; see the answers to mathoverflow.net/questions/21606/…. | |
| Aug 14, 2013 at 17:14 | history | answered | Joshua Grochow | CC BY-SA 3.0 |