> I proved the fourth theorem. It seems one hypothesis is not needed. That's impressive, it didn't cross my mind that one need not assume the second operation to be closed.
> This proof is way too long so probably I used a very inefficient approach. I'm also surprised at the length, given that the proof I know (from wikipedia...) is quite short. In hindsight, I probably should have split the task into smaller subtasks anyway, maybe I will do so in a revised version of the problem set. -- You received this message because you are subscribed to the Google Groups "Metamath" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/metamath/a2d2bac0-8e5a-408f-b6be-6175e3c54755n%40googlegroups.com.
