Difference between revisions of "Notes:Coset stuff/Quotient group"

Latest revision as of 15:57, 26 October 2016

Problem

I really want like a categorical approach to the quotient group. Not "and look, if we take a normal subgroup then the cosets form a group, how lucky!" the nearest I've got is:

• Applying factoring to:

  $\xymatrix{ G\times G \ar@/^3ex/[rr]^{\pi\circ\otimes} \ar[d]_{(\pi,\pi)} \ar[r]^\otimes & G \ar[r]^\pi & \frac{G}{K} \\ \frac{G}{K}\times\frac{G}{K} \ar@{.>}[urr]_{\overline{\otimes}:=\overline{\pi\circ\otimes} } }$

  • Such that $\overline{\otimes}$ is a group operation on $\frac{G}{K}$ and $\pi$ is a surjective group morphism.

But that feels very weak.

It is however without a doubt what we're doing. The normal-groups requirement pops up when trying to show that you can even apply factoring to this case.

$\pi:G\rightarrow\frac{G}{K}$ is the canonical projection of the equivalence relation, see the parent page (Notes:Coset stuff) for information on that.