Timeline for Counterexamples in universal algebra
Current License: CC BY-SA 3.0
6 events
| when toggle format | what | by | license | comment | |
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| Jan 12, 2014 at 7:04 | comment | added | Victor | @Joël: well, before this example, i was very sure that universal groups of subsemigroups of free monoids must be free (subsemigroups of free monoids are of course not necessarily free), since subsemigroups of free monoids live inside free groups and kind of their universal groups would be some subgroups from the free group. Well, semigroups are just crazy wild objects! | |
| Jan 11, 2014 at 1:30 | comment | added | Joël | Okay, I get it: the analog of Nielsen-Schreier for monoids is false. Sorry for having been thick. | |
| Jan 11, 2014 at 0:57 | comment | added | janmarqz | @Jöel: $({\Bbb{Z}}\times {\Bbb{Z}})*{\Bbb{Z}}$ is free product, but isn't a free group. | |
| Jan 9, 2014 at 15:51 | comment | added | Joël | So Nielsen-Schreier theorem is false ? | |
| S Jan 9, 2014 at 8:05 | history | answered | Victor | CC BY-SA 3.0 | |
| S Jan 9, 2014 at 8:05 | history | made wiki | Post Made Community Wiki by Victor |