Скачать или смотреть What is...a (normal) subgroup?

Goal.
Explaining basic concepts of (a classical course in) algebra in an intuitive way.

This time.
What is...a (normal) subgroup? Or: Why care about the difference?

Disclaimer.
Nobody is perfect, and I might have said something silly. If there is any doubt, then please check the references.

Slides.
http://www.dtubbenhauer.com/youtube.html

Material used.
https://en.wikipedia.org/wiki/Subgroup
https://en.wikipedia.org/wiki/Normal_...
https://gowers.wordpress.com/2011/11/...
https://math.ucr.edu/home/baez/normal...

Subgroups vs. normal subgroups.
https://groupprops.subwiki.org/wiki/S...
https://math.stackexchange.com/questi...

Translation group.
https://en.wikipedia.org/wiki/Transla...)

Tetrahedron.
https://en.wikipedia.org/wiki/Tetrahe...
https://groupprops.subwiki.org/wiki/S...

Mathematica.
http://demonstrations.wolfram.com/Rot...

Pictures.
https://math.stackexchange.com/questi...
https://i.stack.imgur.com/ABfLZ.png

#algebra
#galoistheory
#mathematics