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Oct 8 at 8:51 comment added Zhen Lin Thank you! I shall have to remember the name of Mal'cev...
Oct 7 at 21:33 history edited Keith Kearnes CC BY-SA 4.0
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Oct 7 at 21:16 history edited Keith Kearnes CC BY-SA 4.0
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Oct 7 at 13:54 comment added Zhen Lin Sorry, a minor point, but I don't quite understand how you obtain a chain of identities of the form claimed. I agree there is some chain of identities that witnesses the hypothesis that $(0, x)$ is in the congruence, and as far as I can tell it seems the exact form does not really matter, but it would be nice to know how concrete we can be about the congruence generated by a pair of elements.
Oct 5 at 12:59 comment added Zhen Lin I think I see how this can be generalised: basically, we are defining a natural algebraic irreflexive relation on the free algebra on no generators and then pushing it forward to all algebras. In some sense these are "constant", and there can be quite a lot of them because the class of these is downward-closed and also closed under union... (In particular, there is a maximal one, both among the "constant" ones and in general. I think the example for commutative rings is maximal.)
Oct 5 at 11:24 comment added Zhen Lin This is even representable! Apparently my intuition was not quite right…
Oct 5 at 4:29 history edited Keith Kearnes CC BY-SA 4.0
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Oct 5 at 4:07 history answered Keith Kearnes CC BY-SA 4.0